I have an RB600 which has been in place around a year, running 4 x r52n, just recently become unstable. All wireless cards are now disconnecting and reassociating.
Changed the external connectors/cables. The box with board is sealed shut with extra bead of silicone around door closure. Never been unsealed in a year.
There has been severe weather/storm with high winds and driving rain.
I assume there has been no recent changes, such as firmware/routeros upgrade?
My prime suspect would probably be the power supply, especially if it was a just barely adequate one to begin with (they tend to degrade over time). With four cards in there, its probably a bit demanding on power.
Also, perhaps there were power surges associated with the storm, which might have pushed the power supply over the edge if it was teetering anyway. (or just plain damaged the power supply).
Another possibility is overheating, of the power supply, the routerboard, or both; with a similar issue, components which were fine when new, have degraded and their tolerances have changed.
I have disabled a couple of the interfaces temporarily, to see if it makes a difference.
There has been a couple of software stable software updates put on, but have now rolled them back to bo avail, will see what happens with half interfaces.
Chances are the capacitors are leaking, the RB600 and RB600A were notorious for leaking capacitors. I have around 25 RB600/RB600A and not a single one has lived past 18 months without changing the capacitors on the boards.