Mods are user-written changes or additions (
modifications) to the game. You subscribe to them in the Steam Workshop for this game. If you don't know what they are, you won't have done that, presumably.
CK2 has seen similar issues, but generally only when a single empire controls a large part of the map and then a war or rebellion breaks out, so there are too many units on the map for the game to cope with.
I'm not aware of a precise parallel with EU4, but let me know if this only happens in a comparable situation here.
ALSO:
DXDIAG is a program you run from the Windows search box on the task bar. After running it will open a window and start collecting info with a progress bar in the lower-left corner. When it completes click the 'save all information' button and save it to a file then attach that file here.
Please attach here your Documents/Paradox Interactive/EU4/settings.txt and pdx_settings.txt .
...
Read more