Warning: Undefined array key "#field_name" in Drupal\tagify\Element\EntityAutocompleteTagify::processEntityAutocompleteTagify()

I guess this makes sense, because in that context the widget isn't working with a field. I'm not sure why the #field_name element property was added in the first place, so no idea how to fix this.

The problem is coming from the element, the field name when it's used as views filter is coming from $element['#name'] instead of $element['#field_name'], so when the element is used in a different context, the identifier would be the name attribute.

Just tested and the warning doesn't appear anymore. Why did you delete Drupal.behaviors.nodeDetailsSummaries from the main widget though?

Thanks Dieter for review.

Why did you delete Drupal.behaviors.nodeDetailsSummaries from the main widget though?

Because this is already defined in Tagify User List module, and when I was testing the bug that you reported about the filter, I was getting lot of errors related with it, when Tagify is used out of the administration theme. So, it was defined twice and it should be only used in Tagify User List module.

It will be included in release 1.2.13