Dragon World (973800)

Hello,
News on steam, which sends me on this site and I am totally lost!
I was hesitant to state my problem here as it is not serious, and I am not sure if it is the right place.

I'm playing on the Dragon World game (not linux), but it was working fine until either a Steam update or my migration to Ubuntu Mate version 20.04.
On my Steam settings is selected "Experimental Proton"

The game starts well, but for some time now, I have to insist more than ten times to get to connect to the maps (different players on different maps of the game) of the game Dragon World and sometimes I can't choose at all, I have to take the one that is willing to open up.
As well as to create a new map to be able to invite.
He does a more or less fast "connecting" then returns to the "online battle" after failure of the connection, instead of opening the map.
Problem that I do not have when I test the games through a game site with the Chromium browser or Firefox.
I also asked steam players who are on windows, they don't have this problem.

I am not "pro".
If you can advise me.
I don't speak english, the text is done with google translator .... sorry.
Thank you

No source file, test, or entry point is identified. Start by reproducing the Dragon World map-connection failure with Proton Experimental on Ubuntu MATE 20.04, comparing failed connections and map creation with the reported browser and Windows behavior; done requires a confirmed diagnosis and fix.