Hosta problem

Newbie here: I have had my hostas for 15 years in their current location and they were transplanted from old stock at my old house. That said, they have survived flooding waters, underwatering, prolonged waits for transplanting and other abuse. Never have I seen them disappear. In cleaning up for spring, I pulled up some debris and the whole plants, or what was left of them, came up without effort. Underneath was this disgusting wet mold like you might see on sour cream left too long in the fridge. In addition we have an apartment building of chipmunks living nearby and maybe a vole problem. Recently, a new housing development replaced a farm across our road and this may be where the varmints are arriving from. I want to replant but am afraid this may be a soil problem and not the varmints???? We sprayed castor oil/detergent on the lawn and thought we eliminated the voles.

The white stuff, without a picture, is a natural process of breaking down mulch to decay so I don't think that is the culprit. It sounds to me like voles.
The other thing I am thinking it could be is your ground was SO Wet that the roots rotted. I have had that happen with other plants once.
Maybe someone else can comment.

Voles love Hostas but crown rot is also a suspect.

I see crown rot is the most severe of reasons as I would not be able to use the soil. is that correct? Should I wait and see if the remainder of the hostas succumb? We will spray the castor oil/dish soap in that area. I do see a hole near that boarder. I did not snap a pic as I was so disgusted. I will see if any is left to take a picture.

If it's crown rot, I think I would try to get a pick-up load of good soil and put it in the area. This would raise the bed up higher (think raised bed) and give the soil more opportunity to drain.
Castor Oil sounds like a pretty severe pest control. Along with the grubs, it also kills beneficial worms and insects which creates soil compaction. Think twice about using the castor oil. There's other ways to get rid of the voles: vole bait for one. A second way is to plant some daffodils in the area. Voles don't like daffodils and will stay away from them. And it may not be a vole problem. Adding castor oil would be creating a bigger problem.
Think through this delimma. Don't act but re-act. Give yourself some time to figure out what the problem is and please keep us posted.

Birder17, I have a hydrangea in that plot as well as a boxwood and a bleeding heart. Can I replant those?

How big is the Hydrangea and Boxwood? It kind of depends on how big your shrubs are. I think you can dig them up but you would have to be pretty careful. Have your hole ready to plant it back in before you dig it up. Keep as much dirt on the plant as possible. Dig up a little away from the plant to get as much root as you can. Water the shrub/s well the day before you dig them up. And of course, water them well after you dig them up. Also, you may have to cut the shrub back a little. The more leaves and limbs this plant has to feed after it's been dug up, the more stress it places on the plant.

Why are you wanting to dig up these plants??

The Bleeding Heart: yes. But I'd wait until it boomed just to enjoy the blooms. Or, if you don't want to wait, you will probably loose the blooms but it would be moved for next year. The more dirt you can get around the plant, the better. Also, dig your hole where you are going to put the plant first before you dig it up.