AFCI Breaker tripping
Swapping breakers as a test to see if the breaker is working is a good idea. If both breakers trip then the only real method you have at hand is to isolated and find the area in the circuit where you are having a problem. 

Isolation is the key. First disconnect the breaker and see if it will rest with no conductors connected. If it does then your problem is downstream. If you can try and figure out the order of the connections of the devices. In other words find the first device closest to the breaker, then the next and so on. Now you can disconnect all devices and begin to connect them together one at a time. Each time turning the power off reconnecting then turning the power on and see if the breaker trips. Once it trips now you have found the area of the circuit that is causing the trip. This will tell you the location of the fault in the circuit. Check each connection and splice working your way back toward the breaker and make sure they are mechanically and electrically sound and polarization is correct. 

Also if you go through stack exchange you will find several remarks about plug-in connections on the back of a receptacle. Meaning make those repairs also.

It is a long and tedious process but the problems can be found and repairs made.

Hope this helps.