The league joining issue is fixed now.
It was only impacting leagues which were split at the end of the season.
Thanks all for your patience, I'm doing this all alone at the moment so it's a lot of work with so many issues to work through.
FYI for anyone interested in what the cause was: nothing sus, just when the league was split some remnants of the teams moved into the split league remained in the old league, so it thought there were more players in the league than the capacity, when there wasn't.
Ҝ丨爪
Why can people join my old pro division (split league) but not the main league?
Also the split league kept all the boosts.
This should have been fixed yesterday, if your league was split before that it may be the case. How many boosts transferred?