join session with second instance of packaged game
start game with a servertravel (to a map that has a different gamemmode if that matters for this case)
in the gamemmode (MyGamemmode is set to default in the level that is being loaded) at begin play going through authority switch so only server does the stuff.
I “get player controller” cast to specific controller bp (that is default for the gamemmode that is the world override for the map so it should be loaded for all)
Then I call an event that is in said player controller. The event (running “on owning client”) sets up the ingame UI (wich correctly works everytime) and then I cast to the specific gamemmode (MyGamemmode, the one where this event got called from) but the cast to gamemmode always fails.