What band are you using? Do you have any reasons to believe that you're having sporadic interference issues? How's your SnR and modulation look for the clients that are having this issue?
When I asked what band, I meant, what frequency, e.g. 900mhz, 2.4, 3.65, or 5ghz... but based on what you've said, I'm gussing that you're using 5ghz. ALSO... you're having this happen on all 3 AP's at a site? Do you have other AP's in the field at different sites that aren't having these issues? I'm pretty stumped here, and no one else is reporting these issue using 15.2.1. At this point I'd suggest you open a ticket with Cambium support. You can do that HERE.
a week back 3 PMP450i ap's located on the same tower started dropping connected subs.
The logs are showing the SM can not get traffic through so it having a "VC error" and reestablishing sesssion. But this can happen for many reasons.
Do you have on AP generating sync for the rest of the APs? Generating Sync is not good to do with multiple APs on the same tower. You need to get GPS sync to all the APs and reevaluate after that.
What can happen with out synchronization, one AP will be transmitting while a nearby AP is trying to receive. The AP trying to receive will be interfered with your own AP.
The clocks will not be exactly the same on each radio, so it will be a bit of a rolling problem. Sometime periodicity of a few minutes where one AP's will completely go completely out of sync and then a few minutes back in sync.
