Sadly it still doesn't work for me.
The link (invite to PL) doesn't appear on the team page of the 2nd team.
I even made a new PL with the 2nd team and tried to invite the 1st team. Then the 1st team page said: team already is in a PL (which is correct). I tried the other way round and then it said "2nd team is already in a PL", which was correct at that time.
Thanks for your help in advance!