Yes for sure, it’s not running the sim clock as an offset from the OS clock but as some counter in the game loop or similar.
(Note that the real time clock is managed by the OS using a hardware cycle clock in the processor and the xbox certainly would have one. The battery backed clock is only used on startup to initialise the OS, I’m sure the xbox has one of these too, they use rechargeable batteries. I’m sure this has nothing to do with the problem.)
The Xbox absolutely has a hardware clock, just like every other modern computer, phone, and console (its hardware is pretty much equivalent to a PC and runs a variant of the Windows operating system). That’s unlikely to be related to this in any way, though.
You know for sure? If yes then why would the time in a cockpit not be derived from that clock and thus would be accurate to the second?
Don’t know for sure if the same problem exists when playing fs2020 on a PC but most PC apps I know make use of the PC’s HW clock.
What other explanation could you think of loosing time (just “lost” 1/2 hour on a 3 hour flight) and loss of time seems even variable? 
The simulation manages its own clock separately from the real-time clock.
It’s already been mentioned in this thread that realtime hardware clocks are used at boot to set the time, which is then maintained by the operating system.
I already posted a theory above, that time spent waiting between frames on v-sync is not being taken into account by the simulation. This would explain why time loss is greater at lower frame rates, and why it happens with more complex airplanes (TBM with G3000) when it doesn’t always happen with simpler ones (C172 G1000).
[Per your notes above the slowdown is worse at 120 Hz than 60 Hz? which… thinking… may throw off my theory. 
Still, I’m awful suspicious that something to do with refresh rate is at issue, and the difference between frames that run under the limit and those that run over the limit.]
[Note also – if the operating system-maintained realtime clock has an issue, then you should be able to see it on the date & time reported by the Xbox in the home screen, settings, etc. So double-check that if you think it is a real-time clock issue.]
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Are you using Developer Mode or made changes in it?
No
Have you disabled/removed all your mods and addons?
Yes
Brief description of the issue:
Time in the simulator is running slowly. Climb rate in FPM is not achieving correct climb rate i.e slow. ETA on route is not achieving real time despite consistent ground speed i.e slow. Flights are taking too long and overall performance of aircraft is slow/low framerate
Provide Screenshot(s)/video(s) of the issue encountered:
Detailed steps to reproduce the issue encountered:
If I fly a simple aircraft like c172 G1000 no issue. If I fly TBM, CJ4 or Carenardo PC12 I get slow SIM rate.
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Build Version # when you first started experiencing this issue:
I think after most recent SIM Update 12
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Do you have the same issue if you follow the OP’s steps to reproduce it?
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If relevant, provide additional screenshots/video:
Do you have the same issue if you follow the OP’s steps to reproduce it?
Yes, I’m on Xbox Series X.
Provide extra information to complete the original description of the issue:
Doing a flight from KORD to KSMF in A320. 4 hour flight in real life, in sim; 5 hours in the air and have not made top of descent yet. No background apps or programs, updates or downloads are running. Used a separate stopwatch to pace the clock on the cockpit panel. In sim clock is running slower by almost a full second. By the time I finished typing this on my phone, I have finally started my descent, 5 hours after gear up.
If relevant, provide additional screenshots/video:
unable to video.
Everyone make sure you have voted in this thread, we need to raise awareness.
SIM is broken, can’t believe more Xbox users have not raged about this.
Pretty sure this is since SU12
Agreed. Had not had this issue prior to the flight i posted above. Landing and taxi was a trip.
Everything was in slow motion and delayed control responses.
Almost parked it inside the terminal because of the lag between hitting the toe brakes and the plane stopping.
Again, never had this lag issue on Xbox before that last flight. I have ALL traffic turned off. I am the only aircraft in the sky.
KSMF is still the default airport in the sim on Xbox.
I have very few add ons, a couple of airports, a few airplanes, livery packs, and LVFR’s Static Airport Aircraft, that’s it.
Going to try another flight later and see if it is still doing it.
I have this exact same issue on Xbox Series X for months now. It’s so annoying.
The only workaround is to actually increase Sim Rate in order to force the clock to be “real” again and, also, make the aircraft regain its real flight duration somehow.
Meanwhile, I have noticed that increasing Sim Rate seems to break things sometimes, like having issues when taxing after landing, ILS landing not working and even crashes.
In the last few days I have finished several flights in the Middle East, from UAE to Israel , OMAA-OTHH-OERK-OJAI-LLBG. To my surprise, the clock and the sim time runs very well, and it looks like nothing happened before (but I DO KNOW it happened before!!!) . I didn’t change any config in game, or the sim rate, the XSX settings, the HDMI mode… nothing changed,but it just didn’t happen. Maybe tonight I should try again in RJTT OR KJFK >_<
btw . In the inibuilds A310.
Yep, I experienced something similar! To me it looks like that a fix was implemented (I am on AAu2 Beta) but still are not sure if it stays this way or if the clock starts going slow again on one of the next flights.
Just a few minutes ago , I had my A310 spawned at KJFK. The real traffic was so heavy and I would say there were more than 100 planes in the airport because the screen was full of the name templates of the planes… Obviously the XSX was having great trouble with so many crafts and the sim was stuck like a slide show.
Well go back to the clock…one tick in the sim ,almost three seconds elapse in real life … OMG!!! It’s terrible. I gazed at the clock in the A310 and… I was on the verge of tears my friends…
Running Flight Simulator here on Xbox Series X after today’s latest beta update and it’s still happening.
Did a flying using the LVFR A321neo from Orlando to Boston. I had to increase the Sim Rate to compensate the “slow motion effect”. Landing and taxing were both an insane pain.
I’m pretty much surprised just a few people are complaining about this.
I am surprised about that too. As soon as it comes to ‘when do I arrive at the next waypoint" or’ when do I arrive at the destination airport’ I need a stable and precise clock. Also with certain procedures in VFR navigation a precise clock is required. I use for example the timer on my wristwatch to determine how long to stay on a leg and if the sim clock runs slower than my wristwatch I might be too early on a turn.
TEMP FIX: CHANGE REFRESH RATE TO 60Hz IN XBOX SETTINGS FOR 95% IMPROVEMENT
I know two people who I fly with (Xbox Series X) who are consistently “jumping backward” on my end (PC). This seems to be happening most prevalently with high-fidelity aircraft.
I think it could be occurring when the CPU frame time exceeds the frame time required to maintain V-Sync, somehow the physics are not scaling correctly in this case.
Please repeat the test with a 120hz display, using an aircraft with complex (cpu heavy) avionics systems, at a busy online airport. My friend was getting 80-90 IRL seconds per 60 sim seconds in this condition. It’s very difficult to fly together, especially any sort of formation flying.
Is V-Sync set to 50% refresh rate on the series X (i.e. 30 on 60hz, and 60 on 120hz screens)? This could explain why players with 120hz displays are seeing the worst of this.
Cheers,
Dan.
I suspect you are right about the frame time vs vsync, but I have a 60Hz TV, nothing 120Hz ever, and I see this problem a lot. Maybe it can help but it’s not a fix.
I’m using a LG C1 and my Xbox Series X is set to 120Hz, with variable refresh rate enabled.
Maybe I should also disable it to test?
Back here to confirm that this really seems to work.
Yesterday I did a flight using the LVFR A321neo on Xbox Series X, using the 120Hz mode, with a LG C1, as I said earlier. I lost almost 30 minutes when flying from Berlin to Geneva. No multiplayer enabled. Only real life traffic.
Today I’m flying again from Berlin, going to Zurich. I’m approaching and only lost less than 1 minute. Using 60Hz, of course.
Finally, three things:
It’s a pain the huge input delay difference using the mouse after one year with 120Hz enabled. It’s a night and day difference in 60Hz.
The Asobo A320neo doesn’t have any issues when using 120Hz, no matter where I fly.
Finally, also must confess I’m really tired of Flight Simulator, no matter how much I love it since the “old” early 2000s days. After every single update we have something new to fight, new issues, new problems. It’s insanely frustrating. Thankfully and gladly I stopped spending money on the Marketplace.
Edit: As I was finish writing, when landing in Zurich I lost about 3 minutes. I was expecting this, since LSZH was literally unplayable for a long, long, long time on Xbox, always crashing in the past. It’s definitely not optimized.
Hey thanks to everyone who has been replying. I have literally given up on FlightSim. I was going to wait till next update.
To those talking about the clock running slowly, what perhaps you don’t realise is your whole sim is slow. For example, set 2000fpm in the autopilot to climb and time it , you won’t get 2000 you will come short by 2-300 feet. Similarly start timing your legs per the ETA and it will take longer than realtime because the SIM rate is about 80%. It’s obvious to me that the Xbox has a bug, plain and simple. It’s trying to maintain a certain level of performance but the result is to slow everything down which is why in multiplayer you are getting left behind.
I just wish someone at Asobobwould acknowledge there is a problem. The reason that not more people are complaining is that they have given up like me.
Whilst I am fortunate enough to afford an expensive PC I am not prepared to spend the money just to play FlightSim. Xbox was a good compromise.
I too no longer use marketplace, hopefully hurting Microsoft in the pocket might make them act or at least acknowledge there is something wrong. I just got a “we were not able to replicate the problem” probably because they just flew for a few mins and didn’t do a proper flight because they are all too busy on their PC,s!!!
Doctor, I did as you suggested, went into Video settings , turned it from 120 to 60.
Tried a flight and sure enough all is well. I reckon that is why it’s a few people with the latest tech struggling.
For now this is the fix.
How do I tell Asobo ?
Thanks
Steve