Hi Will - if re-joining helped, that may be an indication that there were some "naked" edges in the model. Those are edges that did not end up getting joined to one another even though they are right next to each other.

The edge filleter needs to know about surface adjacency so naked edges will prevent fillets from being formed in that area.

If you see that happening, if you can remember how that object was constructed please let me know, because that construction command will need to get tuned up to make sure those edges are properly joined.

I did have an example of this just recently where this can happen when using Boolean Union on surfaces that are touching edge-to-edge (instead of in a situation where the pieces are intersecting and pushing through each other). I should be able to fix that one up, but if that is what you are running into that can be fixed by using Join to glue surfaces along overlapping edges, rather than boolean union for that particular kind of thing.

- Michael