Hi Rico - similar type of thing as Mauro posts above (he beat me to it!) -

The problem is the existing segmentation of faces there makes for a bit of a difficult overlap area in the fillet in this area here:



I got the above fillets set up by separating your model into individual surfaces and selecting 2 surfaces at a time and running fillet, that does a somewhat different surface/surface fillet operation which is calculated between surfaces and not by tracking along edges. So I could see from that, that there is a kind of overlap area between the fillets and the regular edge based filleter does not seem to be doing a proper job of dealing with that overlap situation.

Since it's segmented topology that is making things more difficult here like Mauro posts a solution is to simplify the topology - here I deleted the segmented faces and built one single surface to replace them, by selecting edges, running Edit > Join to glue them into some new curves, then running Rebuild on those curves to make the to be single segments, then Loft between them. With that in place that sequence you posted above should then fillet more easily:



- Michael