mesh_rssi_threshold

Unless something is crashing (you say there is no indication of this), then in my experience the mesh links are breaking down probably due to interference or dropping signal strength for what ever reason.
You need to set:
mesh_fwding=’1′
mesh_gate_announcements=’1′ on at least one device but all 3 would be fine.
mesh_rssi_threshold=’-80′

The first two allow the mesh to reconfigure itself and self heal its layer 2 “routing”. On startup these are effectively automatically set temporarily, but if something goes wrong, a wireless restart is required without permanent setting.

The last sets the minimum signal strength required to stay in the mesh. In a noisy environment you might have to tune this one, -75, -70 until it is stable – this also effects range of course.

These HAVE to be set using the iw utility though, at startup and after a wifi command or network restart. They do not take effect in the uci config as they have to be set AFTER the interface is up. They are conveniently put in the config so you can run a script to pick them up and set using iw. I just run a background process that checks every 30 seconds or so and sets if necessary.

Of course you might have some other problem here, but….. works for me with what looks like the same symptoms.

iw dev mesh5 set mesh_param mesh_rssi_threshold=-70
iw dev mesh5 get mesh_param mesh_rssi_threshold