Sorry for the slow reply, I was away. I want to fix this properly, so three things if you don't mind:
1. There's a log file at %APPDATA%\dev.gl2mp\Local Store\gl2mp.log - paste it here or send it to yurnior. on Discord. That file will tell me exactly what broke.
2. Did you use the Gacha at any point, and its "Add Slot" button? It's the one thing in the mod that writes into your own character slots.
3. Does Gacha Life 2 itself open normally when you run it without my mod?
One thing worth knowing: your characters aren't in the GL2MP folder, they're in %APPDATA%\dev.gl2mp, which is why reinstalling didn't change anything. Nothing is lost, and there are backups in the save-backups folder in there.