Has you can see in the first image,
the main cylindrical object has two protrusions. The one on the far right had a FilletEdge command performed on it, and had a correct end result, then panned the object to be able to see the left one, and requested the exact same command on that protrusion
with the exact same parameters. However, the end result was completely different, and not as it should.
I repeated the command after checking for any imperfections on the original object. Couldn’t find anything wrong. The same weird errors again. Any idea why this happened? What do you advise to try and resolve this issue?