As the title says the game freezes when opening a new program (Firefox, Notepad++, VLC etc) if I'm playing in Windowed or Max. Borderless Windowed mode. It does not happen if I play in Full Screen.
Note that the game does not freeze if I change or open new tabs in e.g. Firefox while the program is running. Only if I open a new process. If I have Firefox open when launching the game, closing it and re-opening it again will freeze the game.
The game does not appear to have crashed (monitored using Task Manager) and in the first few seconds after forcing the freezing I can mouse over buttons and links and get the "hand cursor", but that behaviour disappers after a few seconds. I can force the game to freeze any time I want, during the "intro"/launch screen, the main menu, during a match, during saving (Fun(?) fact: I am able to successfully load the save game afterwards).
Tried the basics you recommend (clearing cache, deleting preferences and verifying game cache (twice - and I get "All files successfully validated)) , but it doesn't change anything.
CPU: Intel(R) Core(TM) i7-6700 CPU @ 3.40GHz, 3401 Mhz, 4 Core(s), 8 Logical Processor(s)
RAM: 16,0 GB
OS Name: Microsoft Windows 10 Home
Graphics card: NVIDIA GeForce GTX 1060 6GB (I run dual monitors)