Is your RM tub outside?. When low-pressure weather systems come through worms like to climb? Maybe they left. If they died you would probably smell them.

How long has it been since you set up the bin and when did you add the worms?

The full moon right with the storm coincided with me finding a swarm of freshwater apple snails that had left the tank.

They are inside. I've had them about 2-3 years.

I'd like to know how do you add the beddings to your bin. Do you harvest whole bin, then replace it with bedding as if it's a brand-new worm bin?

If so, the worms may be in a shock because it's sudden change in environment so they may be grouping in particular spots at bottom level that is most comfortable for them and you're missing them.

If you're seeing new castings when you turn over the beddings, they're still around.

If you really believe your worms are dying somehow, you can "reharvest" the bin and sift through it to look for the worms but it'll disturb them though. So look for castings instead.

I use a small plastic trowel to move the stuff and worms around. I was told this wouldn't hurt them. We just use a few for fishing now and then and leave the rest alone. I don't remember seeing castings. How big are they?

This is what a pile of worm castings look like:
http://www.friendlywormguy.com/news/worm-beds-and-harvesting-worm-castings/