Very odd as the game itself did not change at that time either! Its most recent patch was in mid-December.
Let's do a full clean re-install:
- move any valued save games elsewhere
- "uninstall" in Steam-Vic3
- manually delete both the Steam/SteamApps/common/Victoria3 AND Documents/Paradox Interactive/Victoria3 folders - In particular make sure there are no files or folders left under either the Steam Victoria3 or Documents Victoria3 locations, before installing again.
- re-install game in Steam, run a Steam Verify when done.
- add Victoria3.exe to the exceptions list of your antivirus app; ESPECIALLY if you have Windows Defender, add it to the Ransomware "Apps Allowed Through" list.
- start the game with no mods active and test with a new campaign, NOT any existing one.
Does that help? If not,
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.
IF dxdiag.txt fails to attach here, rename it to dxdiag.log , or zip it up.
Please attach here your Documents/Paradox Interactive/Victoria3/pdx_settings.json .
From your Documents/Paradox Interactive/Victoria3/logs/ folder, attach here system.log , error.log