Wow, thanks for such a detailed reply.
To answer the points raised:
The main access point I have seen failing is the only AP on the switch, the others are powered from other switches.
The antennas are all internal.
This is a large yacht, 60m in length.
The power is derived from a UPS, the grounding is sound.
My analysis was done with all radars powered down, I did a spectrum analysis and it was clear, no rogue signals.
I did mention 22 access points to start with, I do have another installation with 22 AP's I might have cross posted, though I do have some issues on that site too.
All very odd.
We have also seen this issue when Multicast is enabled. As the WLC will flood Multicast to all APs by default, if you are able to food the WLC with enough multicast traffic it tries to flood to the APs which can't handle the amount of traffic they are reciving and will end up failing to send and recieve the heartbeat messages and the AP will drop off the network.
In the specific instance we saw this it was HD TV being flooded using IPV6 as a test, preventing the Multicast traffic hitting the WLC resolved the issue.