You do the go to window mode, move the window around, then full screen HDR fix right. Because HDR is bugged at the moment and you have to do the above to get HDR working. If you open up options / developer mode, turn it on and turn on the little window that shows fps and main thread, you’ll see at the top it will say either SDR or HDR. If its says SDR then that would explain the lighting issue. I dont know about the GPU/CPU usage since I never checked performance monitor when it was happening. But it could be?
Just because you see 600mbps on a speed test doesnt mean your getting 600mpbs to the server. If you want to check that get a copy of pingplotter and install it. Then open the sim, start a flight, and either sit on the ground or fly on autopilot, then go into task manager/performance and click on the bottom left of the screen the Resource Monitor. Find flightsm in the list of programs, click on that so your only seeing the machines that the sim is connected to. Now write down the address in the box under ethernet (should be 5) then quit everything sim task mon resource man etc, open pingplotter, then put those address in 1 by one and watch it run, if you you see connections that have high latency or packet loss then that could be your problem as well ( dont worry about machines that dont respond at all, those are usually busy routers that are programed not to respond to you requests for security reasons).
No if you see High Latency on any of the connections, and the problems machine(S) are on your providers network, call and complain, it will take awhile because most level 1 tech’s are useless, but eventually if you persiver you might get it taken care of by them. If its off the ISP’s network theres nothing you can do about that.