As far as I remember, in that case you still will be able to get a directory handle (with appropriate permissions), but calling FlushFileBuffers() on it is going to fail.

So you can test for that in advance before the restore and switch to syncing each file individually. Or accept that the approach only works locally and do nothing more, since durability over SMB is a questionable thing.

It's actually quite amusing how modern OSes can abstract, speed up and hide away those things that are still slow even on nowadays hardware.