PowerApp forms get stuck on "Getting your data..."

I was also stuck on this and just figured it out as I was in the process of writing a post here, so I'll explain it for the sake of anybody else who comes along.

The part that was missing for me was on the CreateItemForm. Click on the problematic screen in the Screens panel on the left, Advanced Properties, and the OnSuccess field. That needs to be:

ResetForm(CreateItemForm); RequestHide()

I guess when I copied from other forms it didn't keep that default, or it otherwise somehow got lost along the way. I kept looking at the SharePoint Integration formulas and wasn't getting anywhere before I eventually stumbled across that.