what does NlTimeoutApiClientSession: Unbind from server mean?

What does NlTimeoutApiClientSession: Unbind from server mean and should I be worried.
example:
05/27 06:45:44 [SESSION] domain: NlTimeoutApiClientSession: Unbind from server \\servername.domain.com (TCP) 3.

It is appearing on a proxy in the netlogon file for communication from a Domain Controller. and the ends 0, 3, 4 or 5.

really just interested in a simple explaination of NlTimeoutApiClientSession if such a thing is possible 🙂