Same here. I've narrowed down and replicate it 100%.
If I'm alt tabbed when a character in my control's turn comes, the game freezes and stops responding.
The same happens if I'm alt tabbed when someone joins a lobby I've created. This effectively means running multiple instances of the game and making a "lan solo" campaign is impossible.
It seems any action that would make windows notify me by flashing the taskbar icon makes the game freeze and not respond. This is extremely irritating. Larian, help please. I've already uploaded the crash report several times. If you need me to upload files or more info, I'm happy to do so.