I have one particular AP that shows 0 Beacons in airodump. I can see the beacons in all the other AP without a problem. So is it even possible for AP to not send beacon frames?
It means the access point is a hidden station which means it does not send any beacons. Airodump knows of the network existence and it's SSID because the clients did revealed it. This is why a hidden station isn't a secure one. As soon as a client is connected at least the BISSD is visible to everyone with a card in monitor mode.