Are you sure that your original RCS deaths were due to not having hiding places? I don't have many hiding places, and mine molt fine. I have guppies too, and I've never seen them kill an adult RCS mid-molt.
It's possible you have other reasons for the death. I just want to ensure you don't end up losing your second batch of RCS because of a mistaken conclusion that giving them some hiding places will ensure they molt without issue.
It may be a good idea to let us know more about their death.
That's the only reason I could think of. Back then I also had a few mollies in the tank. I would see berried females but the eggs never hatched just slowly disappeared. Then I occasionally would find a shell of one, but I never got to see them after they molted. This went on until I just didn't have anymore slowly over less than 3 months.
I have slightly hard water, kept cuttlebone in the tank for them to munch on. I wasn't using any fertilizers back then so I wasn't adding anything with copper (unless its in my water already, I just thought about that should I get a copper tester?).
The only thing I could think of was not enough hiding spots during molting so their frail bodies were exposed for fish and other shrimp to torment them in their weakened state. I could be wrong but I do not want to kill another batch of RCS.
So far in hopes of getting RCS again I have been adding live plants, rock caves, pvc piping, all in hopes of giving the RCS a fighting chance.
thanks for the input. I'll be ordering 3 or so nerites in the future after my other tank is done cycling, hopefully I can find a seller that has nerites, RCS, and anubias so I only have to make one order