Hi Dooki, thanks for sending the file!

It appears to be some kind of error in the filleter when it tried to do an optimization of making an exact torus fillet piece rather than the general case fitted surface one. But it appears to have put an incorrect trim on it, or generated the torus shifted a little bit from where it is supposed to be because the trim edges are a little distance away from the actual underlying surface which is what makes for that strange result.

I've e-mailed you back a fixed up version where I deleted those particular bad fillets and used sweep to fill them in with some proper surfaces, I think that version will solve your immediate problem, please let me know if it doesn't.

Unless you happen to have a pre-filleted version of this, I'll have to try and deconstruct your object to see if I can reproduce the creation of the bad fillet. Sometimes it can be hard to kind of "unwind" back to that state though. But to really debug it I need to be able to trace through the steps that are happening when the fillet is being created, rather than only looking at the end result...

- Michael