This is a very odd problem and I have been able to reproduce it easily. After playing Rainbow Six Siege (seems to be happening with Ghost Recon as well), the game refuses to start, crashing to desktop w/o an error message. Investigating the Event Viewer I’ve found under System tab the following error: DCOM error 317. Basically the game fails to connect with the servers.
The only fix I’ve found so far is a bit hard: creating a new User Profile for Windows. Anyone ran into this issue?