There was no option for joining the new season started today where you can earn special temple buildings the Join button was inactive. I thought that's because I am not at that level where you can build temple buildings. So I continued in the Megalopolis League. After accepting the first assignment I returned to the Season screen, just to find that the JOIN button became active. I pressed JOIN and went back to the assignments screen. I found , that I was still in the Megalopolis League. I went back to the Season screen, but now it seemed that I am not in the Season anymore. It says Season starts in almost 7 days. What's up with that ?
