The client now reads the files from a different directory. Previously it was reading them from %localappdata%\Plutonium\storage\t4\players, now it’s reading them from %localappdata%\Plutonium\storage\t4\players\profiles\$$$.
To reapply your previous stats and classes, you could follow this process:
Press Win+R, copy this directory %localappdata%\Plutonium\storage\t4, paste it into the window that opened, then press Ok.
Open the players folder.
Select the following items if they exist and copy them:
mods folder
mpdata file
mpdatabk0000 file
Open the directory profiles\$$$. If it doesn’t exist, either create it or open the game.
Paste the items copied from step 3 into the directory opened in step 4. If prompted to replace or skip files, select the replace option.
This should apply your previous stats.
If you also want to apply your previous class names and settings, go in-game, open the console, and execute the respective command for the mode you’re on:
Multiplayer
exec plutonium_mp.cfg; vid_restart
Singleplayer/Coop
exec plutonium.cfg; vid_restart