Hello Rick,
Thank you for your reply. We have more customers CUCM clusters on this polling node. these seems to be fine. the Issue is only with this customer server. I haven't mentioned that customer has only one publisher in cluster. No subscriber is deployed yet. There are up to 50 phones registered and used in this moment.
I restarted cluster collector several times, but without change. Also I previously removed and added this publisher again into this polling node, but the situation was the same- no server health information.
sumary

error is coming only from this publisher
no other customer's cluster configured on this polling node affected with this issue
no other nodegroup error found
Thank you
Martin