I broke a view by adding the "flagged" relationship to the view, then filtering by the flag_id, then deciding against it and removing the relationship. The filter for flag_id was not removed when the relationship was removed so now I get an error on that view -- "The website encountered an unexpected error. Please try again later.".
The actual logged error is
Uncaught PHP Exception Exception: "No entity type for field flag_id on view frontpage" at ".../core/modules/views/src/Plugin/views/HandlerBase.php line 712"
I intended on going into the database to fix this but I feel like that's the nuclear option.