Sims Freeze Upon Entering Save

Have you tried the "usual" troubleshooting tips including, and specifically, renaming your The Sims 4 USER FOLDER (the one located in Documents where the Mods folder is), launching the game so it creates a new USER FOLDER and checking if what you're experiencing is happening in a new save with a new household?

Also, try going OFFLINE in the EA App and in-game. Server connectivity can negatively impact gameplay (even though this is a single-player game). I've never had it impact gameplay as bad as you're describing but I have had my framerate tank from 60 FPS to 30 FPS.