Graphical problems on Switch when joining another game

We have to Switches and two Minecraft games on each. Now when I open a game (doesn't matter if online or local multiplayer) my wife can join without problems.

 

But when she wants to join me she gets graphical problems on her Switch. Please take a look at the pictures. These problems affect the loading screen, the main game where the highlighted box on the bottom screen looks weird, and also other menus. And when she wants to open the settings menu her game crashes completely and needs to be started again.

 

Since I play more on my Switch it's no option for us that she opens her world for me to join. It shouldn't matter who is the host and who is joining anyways.

 

We tried to change the ressourcepack but it didn't change a thing.

We deleted the game twice and downloaded it again which did not help, also.

And we started our Switches new - not only from standby but after a real shutdown.

 

Other games like the "old" Minecraft Switch version run fine.