I talked to MikroTik support and they advised to set the distance to "indoors".
/interface wireless distance=indoors
and since then everything seems to be fine.
Well Hell, that should have been obvious to everyone! The next time this critical link in our network decides to come back up and i can reach the device at the other end, I'll be sure to give that entirely non-random incantation a try.
How can you release software with as fundamental a feature as bridge/dynamic mesh mode simply failing whenever it feels like it, and even rebooting doesn't clear it up?! These bogus "management protection failure" messages are really ticking me off--not to mention my customers, who don't appreciate being offline for 20 minutes at a time until these outages decide they have had enough fun for a while. While the link is down, NOTHING that I do makes a bit of difference: running a scan, connecting as a station bridge then going back to bridge mode, disabling and enabling the interface, leaving it off for a while, rebooting the RB, even disabling management protection.. The radios simply refuse to talk to each other for a while, and then without warning they go back to working again--sometimes for several days, sometimes for only a few minutes. But if you change anything in the radio's settings, the connection drops again, and stays dropped until the stars align themselves again.
This is supposed to be technology, not magic.
I'm running 6.7, and don't plan to install any more "upgrades" until I hear that this one has been banished--preferably without having to change obscure settings.