Just to add another variable to this discussion about ISP throttling.
I’m in the UK using Virgin media cable at 300MBps down / 30MBps up.
Have been on that service for the last 3 years, and was on their 200/20 service for many years before that.
These are advertised as unlimited services with no traffic management unless there is a problem collecting your payments. I pay by direct debit and have never missed a payment.
I have often tested my speed at various times (usually at least twice a week, using the google & ookla speedtest sites) and I have always had around 310 Down and 30 up. Has been very reliable up until about November 2020.
Since then I have had very variable speeds at set levels from 0.2 MBps, 20, 40 80 & 120MBps and eventually back up to the full 300MBps.
I know when it goes down to 0.2 if i’m flying, as I get warnings about insufficient bandwidth for photogrammetry
I have tried all the usual troubleshooting suggestions from the ISP support website e.g resetting router to factory defaults, changing the Cat 6 connection cable, checking the coax cable is secure etc… but nothing has stopped my connection from becoming extremely slow on occasions.
All my recent MSFS updates have so far been downloaded at between 200-300 MBps so I have no problems with that.
But I’ve now noticed a pattern, if I test my speed and it’s at the full 300 when I start flying, after about 2 hours it drops to about 120, another hour it drops to 80 and then each hour after it drops until it gets to 0.2 MBps.
It then remains at that low level for a few hours before creeping back up again. Leave it for 24 Hours and I’m back at the full 300MBps.
If I don’t use flight sim at all it stays at 300 (tested it 3 times now with periods of up to 5 days with no sim usage). I occasionally play another online game called Planetside 2 and I can stay connected to that all day and remain at full 300 speed.
Connect to MSFS and after a number of hours my speed drops as I described above. The only way to get my speed back up is to not play MSFS for 24 hours.
Seems very much like ISP traffic management to me but their support people are denying all knowledge of any.
I am currently awaiting a new router from them to see if that cures it, but I doubt it very much.