It started tonight. In essence any public T16 game I try to join pops that error 3 times over and then … nothing, back in the game options / join screen.
The only mentionable thing was the last game I joined before the error was a T16 public bounties game, where all the bounties were already completed. Very odd, never got autojoined to fully completed bounty game before… Anyways, back to GW2 and season 28 is apparently over for me.