Hello
Couple of days ago I had a problem with my CPU temperatures (restarts etc.). One of them just ruined game performance in next run, FPS are much lower, game quality also turned worse. My computer was taken to service and no problems with CPU or GPU was diagnosed. Also in other games (Dirt Rally, Mudrunner, Divinity Original Sin, Watch Dogs) there is no problems with performance so I am almost sure that my game files was a little destroyed. I am gonna to unistall Forza Horizon 4 and download it from Microsoft Store again, but is this possible to keep my save and settings and load it after reinstalling process?
Also, my PC isn’t bad with 32GB RAM and 8GB GPU. I’ve been playing Forza Horizon 4 since four month with everything set to maximum/ultra/extreme and I hadn’t any FPS drops even for a while
Your game is saved in the cloud, I’ve transferred mine several times across console and multiple PCs. I’m not sure if 100% of settings are transferred, though.
Just make sure it has fully saved before uninstalling. Run the game up, exit, and look at network activity in task manager to be sure that the xbox live game save process has completed.
Also note that the process is not risk free. When you reinstall and run the game up, it will take quite a long time to download the game save, and you mustn’t interrupt this process. If you had a power cut, for example, during that time, you could lose your game save.
Okay, thank you. Can I load game in another way after reinstalling by copying and pasting wgs folder copy in it’s place (AppData\Local\Packages\Microsoft.SunriseBaseGame_8wekyb3d8bbwe\SystemAppData)?
Yes that should work, it does for me. It should be unnecessary, but it would save you the time waiting for it to resync from the cloud which can be incredibly slow, regardless of your internet speed (ie. an hour potentially).
I don’t see any reason why you should need to reinstall the game though, I doubt anything is wrong with the game files. But there is nothing stopping you trying.
I believe there are people on this forum who have successfully backed up and restored their local copy of the game save, but bear in mind that isn’t something that is officially supported, as you can imagine the scope for exploits. If one of them sees this thread, maybe they’ll respond with more info, but the cloud save has worked fine for me, though it can’t hurt to save a backup of the local save, just in case.
I reinstalled the game and now everything is working fine - no lags, no worse quality, 60fps all the time 
My save from cloud also worked, I think I have all the cars, decals, clothes and custom routes on it’s place. Thank you all for help