Yeah I had been thinking something was misaligned by some small amount there which is probably what is giving the filleter more difficulty. When you see a "flat" snap being engaged on something that should be flat (like Scooter shows above), it means it was not actually all quite flat. And if you do the reverse and try to stretch it out vertically rather than flatten it, some edges on the inside circular hole that get stretched out so it seems that it's probably those edges are on a bit different z level than the actual plane surface. I had taken a close look at your outer outline before and that one looked fine if I remember (meaning no flat snap engaged on it so it was already flat).

Anyway, I'm also able to repeat over here that once the top face is separated out and trued up to be totally flat and rejoined back in the fillets go ok after that.

Thanks Scott!

- Michael