Bug with Stacking In my own module "1941 : Operation Barbarossa"

I created my own Vassal Module for 1941 Operation Barbarossa
And sometimes the stacking bugs, the double click doesn’t work
I need to reverse the counters and it’s OK

Photos A1 & B1 = bug
A1 A1
B1 B1

A2 & B2 with reverse it’s OK
A2 A2
B2 B2

The counters in the top hexes are not stacked together, but are sitting close to each other.

How are those counters arriving in the hexes?

Do you have snapping to the grid turned turn on?

…and are the counters all in the same Game Piece Layer ?