Depending on the type of African cichlids you have you may be able to stock more, that may help. I have 30 Mbuna in a 75g and also had the same problem. I added some holey rock and some large barnacles and they started swimming around more. So try adding more rock work.
Your problem may also be as simple as an aggressive fish. I had an auratus for a while and as soon as he matured all the fish hid in half the tank while he roamed in the other half.