Here it is : https://bugs.launchpad.net/snapd/+bug/1884849
Now I found a little issue in Gimp, both on 16.04 and 20.04 so I suspect here it may not be related to snap itself :
⋅ tools-group does not work as expected. Whatever setting I choose in preferences
I always have to click on a group-tool to show the list of other tools.
I expect this list to show on mouse hover.
In this situation, first click show the list, second click enables one tool from the list. It’s one click too much.
And other side-effect is now, if I want to go from one ( enabled ) tool to another one, I need to click twice and not reliably…