Krass..let me show you a simple example about fillet in a situation with-without seam

A simple polyline 20x20mm:CENTER= corner filleted 10mm,RIGHT= corner filleted 10mm then REBUILDED



extrude now both:rebuilded curve on the left don't have seams,right curve show origin of the seams



now put two cylinders in a particular position





select both edge loops



Fillet both



Now you know,before fillet always check the area,if you detect seams crossing each other and so,rebuild surfaces avoiding that.

For further advanced situations check this:

https://vimeo.com/63076359

M