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.
If you have updated I assume you have overriden the changes Hugh made?...The autofill plugin was never designed to work with repeated groups...
Do you have a backup?How can I recover the changes?
OK, it'll be a day or two before I can look at this again, I'm in the middle of putting out a new release.
-- hugh
I really thought that the changes were include in the last update.