i too, have recently clean built my WIndows 10 machine...I have exact same problem, I went in under smb:// < IP > and everything on my Win10 machine is accessible... APART FROM the 'shared' USB Drive smb:// < IP > / < USB Drive Letter > (which is where a majority of my files are).
Everything shared from win10 has full control permissions set including the USB Drive I cant connect to.
Regardless of which way round I attempt to access it on the Pi3, I get the failed connection OSMC window stating 'Path Invalid' iirc. Will try the FSTAB trick hopefully at some point this week but dont hold much hope.
Has anyone had or solved this particular issue with USB Drive shares, when HDD drive shares work perfectly well?
Sorry for thread hijacking but didnt see any point in starting yet another thread for an almost identical issue.