The AREDN devs have uncovered a memory leak in the dnsmasq module. AREDN inherited it from the OpenWrt folks, but to be fair they inherited it from the dnsmasq project.
Symptoms: Eventually the nodes run out of memory and start randomly killing stuff, resulting in various failures which seem unrelated. How fast that happens depends on how much churn there is of nodes coming and going on the network. So if the network is very stable, it might take weeks before anyone sees it.
If you see these symptoms, the fix is now in today's nightly builds (both babel- and babel + OLSR).
The fix has been sent upstream to the dnsmasq folks; hopefully they'll see fit to include it, or fix it some other way for the future.
Orv W6BI