I've had this happen a few times now on sites where I couldn't run NV2 from the start because of mixed clients, where the site runs fine on 802.11 and then suddenly most (usually not all) client CCQs just plummet. Then I'd try the usual frequency changes, realignments, kicking off random clients to see if a radio got busted, other random tweaks I try think of at that time, but things will usually just stay the same.
Then I'd quickly switch over to NV2 and bam, CCQs climb to even higher than before and I go swap out the usually one or 2 UBNT clients for a Mikrotik device. This has happened to me 4 times already.
To my limited knowledge this is either due to collisions happening or a superior? way NV2 handles noise? Any one with more experience and knowledge that can maybe give me some insight into this?
We run a mix of Mikrotik radios: Baseboxes, Netboxes and Mantboxes. I usually use UBNT sectors on the non-integrated units. We run in a hilly/forested area so most of the time clients can't see each other if that matters. (Try not to run things at full power but our "neighbours" usually don't follow this practice.)