I have a support ticket (#02569292) in for this and Esri cannot duplicate it. I am surprised others are not posting on it because we have this happening in multiple Enterprise geodatabases where a split of a polygon creates a null geometry record. Sometimes you cannot get rid of the record. I've also been able to replicate this in multiple hosted polygon layers agol (editing them in Pro). A video of this on a agol hosted layer included, and an image from an enterprise based polygon layer too.
If anyone has any ideas, we'd like to hear them - we're stumped!
btw, this is not on every split done in Pro. it's intermittent.
