Here's the first part of the story. Summing up, existing wiring was put on AFCI breakers. Some outlets had hot/neutral reversed. Electrician corrected this.
Now, the front porch light, not part of work that electrician performed, trips two AFCI breakers! The lights go off in the two of the bedrooms and the hallway outside the bedrooms. The two bedrooms are where the outlets had hot/neutral reversed. I didn't test the all receptacles to see if they have power. Each room had one receptacle that didn't have power.
What could be happening? How do I go about debugging this wiring? What are the steps?
Update Found this Siemens guide for troubleshooting. I have the Siemens QA115AFCP single-pole 15-amp Combination AFCI Breaker.
Update The house was built in 1939. There are metal junction boxes in various places (I've seen them in the attic). There is metal conduit that runs between junction boxes. I don't believe they are grounded.
Update 1/15/17 I tested all of the outlets in the house. Here's more info. All of the outlets in the living room (and one outlet in the adjacent room that shares a wall with the living room) trips the two AFCI breakers when I plug in a light and switch it on! (Is it basically one offending wire that feeds all of those outlets?)
Update 1/16 The electrician checked it out and said that the wiring consisted of two hot lines and a shared neutral. He's rewriting two of the rooms that we're tripping to have their own home run.
Update 1/17 The electrician fixed the situation and ran a new home run with an AFCI breaker to the two bedrooms. He also discovered that the forced air heating unit was wired with a shared neutral so he also ran a new home run to that (with a normal breaker). The living room with outlets that tripped an AFCI breaker, they wired to a normal breaker.