Hi Glenn, I also tried reconstructing your object at it's existing size by lofting new surfaces, and this new version also seems to behave ok for filleting (attached).

Maybe what you have been running into is a previous bug in Loft where it would sometimes not generate a tight enough fitting tolerance and not make a quite accurate enough result.

That was a bug that was fixed though in the most current v3 beta, are you running the Jun-27 v3 beta version or are you possibly running an earlier version than that?

If you happen to have the original curves that you used to construct that top piece, could you please send those over and tell me which specific method you used for the construction? That might help me to figure out what was different about your original model you posted versus the one I constructed and attached here...

- Michael