It wasn't the real-time sync either.
I ended up noticing that there was a small time discrepancy between my cell phone and my PC (well, all servers, and clients, as they're synced w/DC), which kerberos seems to have taken great issue with.
I manually made the change to time and date within the DC (domain controller [virtual], which is also my time server for the domain), but saw time 'slipping' following Windows updates, etc. and would again have to manually change settings to correct, despite my time server being synced with MS' time server.
I traced the issue to the logon script that I inherited, which was originally employed with our previous Windows Server 2003/2008 R2 environment, and called
net time <DomainController> /set /y
This isn't necessary with modern time server (W32TM) implementation, and ultimately caused the time bust across the domain (more to it, but that's the takeaway).
In any event - the issue has been resolved now for a week or so, without another instance cropping up... and the server is generally operating much better in terms of performance with the same 5-80 MB drawings... so, yay.
Cheers