IAP-215-RW single node. A little hard to describe, but here goes...
I have a doorbird ip doorbell with camera feed. The html widget works ok, and shows the camera feed fine. The iOS app fails to connect, instead it keeps disconnect/reconnecting without success. While this occurs, the AP cpu maxes out at 100%.
I've found that changing the allowed services (Airgroup, airprint, airplay, DLNA etc) can change this outcome. Initially, when the fault was observed, all options were enabled - all four AirGroup checkboxes, plus all AirGroup services. Turning everything off resulted in the iOS connection to succeed although it's difficult to nail down the exact service or pattern, this seems sometimes require an AP reboot or the passing of time to before a config change can be tested.
The last 'fix' required unchecking Bonjour and DLNA checkboxes.
I realise this is vague but thought I'd pitch it here. I've asked the other vendor for info also.