13 days ago - AndrewT - Direct link
The current 1.31.x patches are definitely slower than previous ones, but not to the extent you describe.

Were there any mods used in that problem campaign?  
13 days ago - AndrewT - Direct link
A video of a game lagging won't tell us anything about what is causing that lag , I'm afraid.

Please attach here the affected saved game. And 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 .
From your Documents/Paradox Interactive/EU4/logs/ folder, attach here system.log , error.log .  
13 days ago - AndrewT - Direct link
I get that problem with that save too, so I guess it's a bug rather than some issue on your machine.

Please make a new thread in the Bug Reports forum and attach that save there for QA to look into.

Sorry for that problem!