I did ask the user and they said it only occured for my add-on, and that they could delete others without an error message. I’m not too familiar with how the other add-on (Migaku Dictionary) works but it throws an error with the “/” key. I found an issue on github with the same error.
I’ll change the name of my add-on for the future but it looks like they are incompatible at the moment. Thanks for the help.