Just bumping this since I see multiple posts about the same issue dated 3 months back.
Has this issue been ongoing for the past 3 months+ and still not fixed?
I switched over from the MS Store version to steam, the game was fine and I could still Alt-Tab, then I installed the Steam Insider build and that alt tabs fine, BUT now the live steam version always freezes on alt+tabbing after I installed the insider build...
That can't be a coincidence, right? something weird is going on and if others can post about their experiences (If they also use the insider build and if the issue has presented itself after installing insider) maybe we can narrow down the potential cause of this issue.
I'd much rather the insider version to lag when alt+tabbing as we don't use that client as much as the live game itself.