STAS - Generally Working OK, but I occasionally get missing clients. Is it possible to add these manually?

I got the STAS Working well, but very occasionally I get clients logging in that do not appear in the Live Users list on the STA Collector.  And Thus cannot be authenticated.

I got these users to restart and relog on, but to no avail.

Is there a way I can Temp Add these clients.  And Why would the problem occur (seemingly randomly)