I'm on version 2.4.19 and the bookmark feature has been working perfectly fine but out of the blue (I've not edited any files on the server) I now get given an error page when changing a bookmark's name and leave the tags box blank

If I change the bookmark's name and leave the tags box blank it goes to this error but If I then go back to my bookmarks the bookmark name has indeed changed.

If I change the bookmark's name and add tags I do not get the error.