[2020] Asset editor problem. Cant save assets.

My guess would be a mod is causing issues. It's always best to disable any mods you don't need in the editors. If you don't need any mods, then you can easily disable them all with the launch option -disableMods

I would also look at mods you have recently subscribed to or mods that have opdated recently since it's a new issue for you. That might help you find the mod messing with things, so you can disable it while in the editor.