I would recommend increasing your SM Receive Target Level to something like -55dBm. The IDLE SM shows a SNR of only 9dB. (A fluctuation in the noise floor of just a few dB will likely knock it off the network.) I think you need at least 7dB just to connect, but ideally you would want this value to be at least 32dB in a perfect world.
SM Receive Target Level is the setting that tells SM's that are coming in too hot at the AP how much to turn down their power. This keeps SM's that are close to the tower from overpowering SM's that may be farther away. Also it keeps SM's that are close to the tower from shooting passed the tower and causing interference for other towers. -55dBm may not be the absolute best setting for your particular configuration, but it should be a good starting point.
The "extra" VC's are from enabling the High Priority channel on your subscribers. It likely will not affect your setup either way. You can disable them just to keep things simple.
The SM Receive Target Level for the AP should be stronger than -75 dBm. Set it to -55dBm and leave it there. (This is probably not your original problem, but it WILL cause an additional problem if this is set wrong.)
Did all of the radios update through CNUT? Or just a few of them?
If there were some that did not update you should plug into each (that did not update) individually to update them.
Also if this is a system that had been working in the past but is not now, have you done a Spectrum Analysis to ensure you are on the cleanest channel?
Additionally it may be a good idea to double-check the cabling for that one SM to make sure that something has not happened. Is it possible that the SM is disconnecting because of power/cabling issues? You should be able to check the SM's uptime to make sure that it is not rebooting causing this problem.
I think the next thing I would try would be to swap two SM's to see if the problem stays with the SM or not.
For instance, swap NE Pole and NW Light. If the problem stays with the SM then you might have a bad SM. If the problem stays at the location then you might try replacing the cabling and the power supply just to be sure.