There is an access point in the neighborhood with a very similar MAC address to one of my Meraki APs. Bytes 2-6 of the MAC address match.
Apparently this is enough for Air Marshal to consider them being the same device:
https://meraki.cisco.com/blog/2017/09/rogue-access-point/
Since the access point in the neighborhood which has a very similar MAC address to one of my Meraki APs isn't broadcasting an SSID, Air Marshall has started associating every AP is sees that isn't broadcasting an SSID with this one and is telling me that there's almost 400 Rogue Access points connected to my LAN. The number keeps going up every day.
This is completely inaccurate. The only thing connected to my LAN right now are the Meraki APs. There are no rogue access points.
I've opened a support ticket and tried to explain the issue but they aren't understanding. I'm at a loss of how to get this resolved.