Thank you, thank you, thank you.
I too was beating my head over this one. Was working great for a long time, then out of the blue, BAM!... dropping drive mappings on my clients.
Even though unraid was set to pull time from pool.ntp.org, my domain controller time server in a Hyper-V server had drifted off by 10 minutes. Re-synced my time server with the same pool.ntp.org server (which it always was with) and then I could rejoin my domain.
For those that are thinking that my Hyper-V Host server needed to have the Integration Services/Time Synchronization unchecked, it was already unchecked. Now I'll have to find out why it drifted in the first place. Also the host server's time was spot on with pool.ntp.org. Another challenge to solve I guess.