This issue is now resolved. SeeUser-ID Agent 8.1.7 Addressed Issues
Windows User-ID agent fails to perform periodic probing at the configured interval, which results in a temporary loss of IP address-to-username mapping on the firewall until the next probe is complete.
Workaround:Configure the probing interval to a multiple of 51 seconds.
After receiving machine account names in UPN format from a Windows-based User-ID agent, the firewall misidentifies them as user accounts and overrides usernames with machine names in IP address-to-username mappings.
The Windows-based User-ID agent does not detect users whose account name (sAMAccountName) contains a dollar ($) character that isn't at the end of the name.