This fix worked for me, I hope it works for you too. I don’t know exactly what fixed it so I’ll list exactly what I did.
1. Navigate to your Ubisoft game launcher folder (usually C:\Program Files (x86)\Ubisoft\Ubisoft Game Launcher)
2. Right click UbisoftGameLauncher.exe
3. go to Compatibility
4. Check Run this program as administrator
Complete the above steps to the following:
I also clicked UplayCrashReporter, UplayService and UplayWebCore – nothing popped up.
Also delete your savegame folder in C:\Program Files (x86)\Ubisoft\Ubisoft Game Launcher
PLEASE NOTE – IF YOU own any other game from ubisoft you WILL lose your save.
If you only own Rainbow Six Siege you will not lose any progress.
1. Close out of Uplay if it’s open
2. Launch “UbisoftGameLauncher
3. launched Rainbow Six: Siege
Let me know if this worked for you!