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 .