Hi Sun, there are some little slivery surfaces in the side walls of those holes, like here:



Having little slivery fragments like that is not good for filleting - it makes for little fragmented fillet pieces trying to be constructed, and it's particularly difficult for it if the little fragmented pieces are not smooth with one another because corner patch pieces are created by the fillter where 2 fillet pieces meet at a crease. That's particularly bad if the crease is only very shallow like 5 or 10 degrees tangent deviation because it makes for a tiny corner piece as well.

So probably those holes will need to be remodeled to be a cleaner more simple surface structure that is just made up of one surface instead of being fragmented into numerous slivers like that. If you can post your model I can demonstrate what I mean by that.

- Michael