Another comment, since I have spent an inordinate amount of time on this and I'd like to spare future users the same trouble...
Phil, when I was working on this yesterday, I didn't quite understand your second solution so I just removed the global variable from my gallery OnSelect property and my edit form's Item property.
Well, wouldn't you know I ran into another problem today where I really needed that global variable in place.
So, I came back to this.
Turns out Phil's second solution is even better than the first (so extra kudos to you)!
As usual, this most infuriating problem had a simple solution -- and the trick was just to find it.
For anybody who runs into this problem later...
IF you are running into a problem where you submit a form but changes don't show up until you re-select the item from the gallery...
AND you are using a global variable instead of the default Gallery.Selected method of choosing and editing gallery records...
THEN the easy solution is to add a clause to your submit button, before the navigate property, wherein you update the value of the global variable (using SET). This basically elbows PowerApps and reminds it that when it goes back to the view screen, it should show you information from the updated global variable item.
Easy peasy.
For what it's worth, my solution was slightly different than what Phil wrote above.
Instead of Phil's suggestion:
Set(Globalvariablename,Galleryname.Selected);
I put:
Set(Globalvariablename,Editformname.LastSubmit);
Seems to be working fine now.
Thanks for getting to this first, Phil!