In case anyone out there is banging their head against the wall about this...
- I spent an hour+ looking over these threads trying to resolve a related issue - I tried to dissolve a layer with tonnns of "slivers" resulting from a union. Result was an "empty output". I tried "repair geometry", it succeeded per results window, so I tried again, same result = "empty output". I noticed the repair tool still showed many fixed features if I ran it again. I then noticed it was only fixing some of my features (was a big file - 60K polygons). I ran it several more times until there were no more to repair, tried dissolve again, and it worked. Oy! Hope this helps.
This worked for me in Pro, and I only needed run the process 1 time, it seemed to resolve numerous errors. I also ran this on a Parcel layer with just under 60k parcels. Thanks for the tip!