The one on the left is Hatori and the one on the right is YS. You can see the difference.

Hatori is 3.6mm section
YS is 4mm section

The Hatori is a loose fit on the header, around 1mm clearance. The muffler pushes onto the header quite easily.

The YS is a neat push fit onto the header, which explains why it is much harder to get the muffler on. Maybe it's a bit too tight? Being that tight, it wouldn't move on the header as much while flying and wouldn't get any oil under for lubrication as the Hatori does. Maybe not moving is causing it to stick?

Possibly the Molykote grease will let it move on the header and prevent it from sticking?