@ybycode could be. I once had a MySensors project which used a speaker. The speaker was very close to the radio and that Node behaved just like yours. When I move the speaker away from the node it became stable. Not sure if an inductive speak could be the cause, when you use the break-out relays. But that's a good question for someone with more electronics knowledge. I've found a tutorial about watch dogs. It is a last resort, but adding a watchdog will reset your arduino if it stalls. It doesn't resolve the cause though. But I'm thinking about adding a watchdog to all of my sensors. Just to make sure they can't stall in case hardware related issues.

Yes, the site is manually updated (improvements is on its way). Must have missed the sleep updates when doing the overview. Doxygen is always the best place/most correct place to look. And we'll probably move over to pure doxygen once it covers a majority of the library.