Hi Andrew,
For me, I’m relieved that my plugin isn’t the cause ?? But unfortunately you may experience this type of results if you are using several plugins that edit the menu. This is because WordPress only has one “hook” we can attach functions to to edit the menu, and if two plugins use the hook then they will conflict. When another plugin uses that same hook, my plugin takes lower priority, it should not do anything when another plugin uses that same hook. I’m not sure though if there are other ways that conflict can arise, through other hooks… I’ll look into that.
I will download the plugin you mentioned, and try it out myself to see where the problem occurs and if I can to anything to limit problems.
Thank you for reporting this. Marking this topic as resolved.
Kind regards,
Diana