I had this problem as well. I wasn't always able to replicate it, but clicking on things (banners, 'OK' buttons, portraits) would seemingly randomly cause a freeze and crash. I have pretty much all the 'official' DLCs with no unofficial submods.
The solution for me was to make sure that the base game was updated to 3.0.1 rather than 3.0. This seemed like a small thing, but I went from having a crash every 5 minutes, to not having a crash since I've done this (~2 hours of gameplay).
Same here, updating to 3.0.1 did not fix but reduced crashes a lot. What else helped to reduce crashes is if there are any big wars happening and i notice game starting to slow down/freeze every month for a sec i reduce game speed to 2 and do not try to quickly click through portraits and stuff as i noticed that triggers crashes more often.
'A Game of Thrones' is a user modification for Crusader Kings II not affiliated in anyway with Paradox Interactive or the rights holders to 'Game of Thrones' and 'A Song of Ice and Fire'.
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