If I press the windows key when the game is in fullscreen or borderless window mode, it freezes and never goes back. The sound keeps playing but it stays on the last image displayed before I pressed windows, and keyboard or mouse imput does nothing. This is especially annoying considering the amount of time the game takes to load (fx 8350 / gtx 1060 / 8gb RAM / HDD) because I would like to do other things like browsing internet during that time, but I cannot, and nearly every other game I play works well in borderless window mode.
If someone at Ubisoft reads this, please correct this ASAP, thanks!
I had this same issue in the first year of release. Windows key and/or Alt + Tab would crash and/or freeze the game. I honestly wish I could remember what I did, but I believe it sorted itself out with a patch or with a driver update. Check your hotkeys with windows and dig through all of the settings in and out of the game.
The other possibility is that there is a conflict with an overlay for another program or with some sort of program that turns itself off when games starts but would activate again when you alt+tab out.