Assuming the AP management is in the same subnet it too would need an ARP entry in order to reply to connections from the client. If pfSense is losing it's ARP entry or has a bad one the AP may well be seeing the same thing.
When it fails do you just see no ARP entry rather than a bad entry?
With no entry it should just ARP for the device to create one.
You should see ARPing entries in the pcap. Make sure you're not filtering them.
If the wifi interface became detatched n the client I imagine that would blow away any ARP entries that were built on it. I would still expect the client to just send ARP queries as soon as it re-attached though.
Steve