ZCM 11.2.3a MU1

I have one PC that keeps dropping out of the list of Workstations.
During testing, I tried zac reg and zac unr and in the process it
unregistered two other PCs. I thought I finally had it fixed. But
now I have two other PCs that think they are registered, but they
don't show up in ZCC. So I tried to unregister one of them so I could
register it again and the unr removed the first PC from ZCC. This
product has been around long enough that I shouldn't see this type of
problem. How do I fix this? I don't know how to get all three
properly registered at this point.