It’s easy see if it’s add-on related by disabling all your add-ons, reloading, and trying again.

There is a very quick way to disable all add-ons from the menu:



In the Add-Ons menu (Escape > Add-Ons), click on the word "ON" next to the smaller "Add-Ons" text. It will toggle to "OFF" and you'll see your add-on list (including libraries) grey out. Then reload UI.

Alternatively, you can quit the game, rename your Add-Ons folder, and then start the game again.

If this is a sudden change for you, do you recall which add-ons you have recently installed?

If not, you can try disabling half your add-ons and leaving the other half enabled. If you still get the error, it's in the half that's still enabled; if you don't, it's in the half you disabled. Keep narrowing them down like that until you've found the issue.