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.
$rowId = $this->formModel->formData[$pk];
$rowId = $this->formModel->formData[$pk][$repeatCounter];
$rowId = (is_array($this->formModel->formData[$pk])) ? $this->formModel->formData[$pk][$repeatCounter] : $this->formModel->formData[$pk];
Try changing line 104 of plugins/fabrik_validationrule/isuniquevalue/isuniquevalue.php from
toPHP:$rowId = $this->formModel->formData[$pk];
I'm not really sure if it ever needs to be checked that $this->formModel->formData[$pk] is already an array.PHP:$rowId = $this->formModel->formData[$pk][$repeatCounter];
If so this line might be the better replacement?...
Hopefully Hugh will see this and he can decide - otherwise I'd change it myself at Github.