Hi !
I realized my mistake, having a variable so that the matching property was always true. Your message confirmed my thoughs. I made some changes (as you suggested) and it worked like a charm. ! Thanks
Indeed, I put the GCK inside the player hand but it is still not working. Don’t know why. Maybe the term “map” inside the “Apply to counters on this map only” refers only to map levels and a board is not considered as one. If someone can confirm that, I would be pleased. Or it could be a bug. 
I wanted to use the $PlayerSide$ parameter to have more flexibility in the player characters. But as you noticed, it could never work since the condition would, in this case, be always true.
A trick would be to use this : https://forum.vassalengine.org/t/player-name-associated-with-player-side/6264/1
In this case, I should have to change Owner parameters (currently characters name) to P01, P02, and so. I’ll give it a try.
Again, thanks for your help !