Ok i googled it and consulted with Andrew
so it seems that sometimes poor water quality or.fish disease like ich, parastes or velvet can cause clamped fins along with other things that stress the fish .. so i suggest this week to do a couple more water changes then normal 25%-50% and rearrange your rocks (to help with the lip locking duo) then montior the water levels and fish for any signs of change.. if that doesnt work then start removing the fish that is in the worst condition to the 29g and swap them out accordingly until the problem is cleared up .. i dont think 2 fish that arent the same (ex. 1 ob zebra and 1 peacock) or even 2 males would be safe in the 29g
Also i would google the symptoms for more information. I just searched what causes african cichlids to clamp fins..