Thats TheTVDB ID, so thats good.
Not finding that IMDB leads me to believe its not being persisted there, which is also good, but I can’t really explain why its there again, unless Kodi is putting it there, but it hasn’t done that previously.
You can certainly try removing a show from Kodi, removing the NFO files created during the export and then re-importing, but I’m not sure if it will help, try with one show and take it from there. I’d suggest backing up the NFOs first, just to be safe.