I have the same problem with user @ArnoLubben in the group Team The Hague: Membership request is accepted but remains in the list "Pending Requests".

I've reported this to support and they can resolve it in each individual case. However, this appears to be a structural problem.
@Markof in the notes of Chess.com Beta, 2018-01-19:
I have club request from player nivckovbrat to club Slovenska liga in allerts. I agreed this but one apears again and again.