For running J!5.1 you must https://fabrikar.com/forums/index.php?wiki/update-from-github/ or include the new file manually https://fabrikar.com/forums/index.php?threads/joomla-5-1-and-fabrik-cannot-find-files-error.54473/post-285151 See also Announcements
Please see our announcement here.
The plugin is attached to the form, so I'd expect to see only one plugin, but it seems that you are suggesting its tied to the groups somehow? perhaps a screen shot of the form plugin settings might clarify things for us?I have 17 groups on one list, each with form upsert plugin.