Posting this for a co-worker:

"Any of you seen RDP access drop from a server and only a reboot fixes
the issue? I think its b/c port 3389 is no longer listening, for
whatever reason, and thus its not accepting RDP connections since it
uses that port. Not much in the event viewers for clues.. also, googled
it, and not finding much of a solution there either (beyond a reboot
which always fixes it b/c port 3389 is now available after reboot)."