It sounds like your cache might be invalid and that’s what’s causing the issues. If you log out and then back in does that fix things? Out of interest which browser / OS are you using? That will help us debug and replicate this on our end as well.
For me, this happens when I am doing a multi-card update, i.e. assigning a new tag if I don’t complete the process, i.e. fail to press done and close the browser whilst still in modify mode when I log back in again it appears. However, logging out and back in clears the error - does look like a browser cache issue.