It’s my turn to report some buggy things happening now.
I just tried to make a party with someone, we were both definitely seasonal characters, both of us showed the leaf icon in the chat. But for an unknown reason i would get the “non-season characters cannot play with seasonal characters” message.
The closest we got to creating a game was when i invited him from the menu. His portrait appeared on my screen after he was able to join as a party, but the portrait was missing his character’s head and i couldn’t see his toon on the menu screen. I was unable to create a game, the message “non-season characters cannot play with seasonal characters” being displayed on the create game icon.
From inside a private game, at first the send invite was greyed out with no message attached. Trying again after creating a second private game, the same non-seasonal message did display this time despite him being able to join my party earlier.
Something about matchmaking, or probably the seasonal character detection, is on the fritz and preventing players from partying up. This all happened while in private game mode.
Seems like they are having some widespread issues with their servers atm.