How to fix intermittent 0x800704cf error when accessing SMB shares on Domain Controller?

We've got an intermittent problem accessing file shares on one of our Windows Server 2012 R2 domain controllers. Occasionally when I try browsing \\servername, I get:

Our other two DC's are fine - haven't had any error messages accessing them at all.

No idea what's going on... ping always succeeds, so doesn't seem to be a connectivity issue.

Static DNS A records exist for all our DC's and all the SRV records are in place. dcdiag /s:servername passes all tests, though there are some warnings:

Starting test: DFSREvent There are warning or error events within the last 24 hours after the SYSVOL has been shared. Failing SYSVOL replication problems may cause Group Policy problems.

Are there any free diagnostic tools available to pinpoint the problem?