My ramshorns are having the same problem. I have read that this could be from the lack of calcium or lime in the water or the water being too soft. I am trying to find information about helping the snails and not hurt the fish. All I have found is to add some sea shell or chalk but this can really raise the PH
as I found out when I added a barnackle shell to my 55 gallon tank years ago and could never get the ph
They seem healthy but the their shells have a lot of "pits" in them and they are getting worse or so it seems. They are laying eggs everywhere over the last couple weeks and I am still waiting for the latest ones to hatch but they are less than a week old so it will be a while. My first cluster was lost as the larger one ate most of them. The newest ones are in a breeder and should stay safe in there.
Will let you kow if I find anything that will help