So Windows 10 1803 update creates another OEM partition. In my case, the new partition decided to take over one of my existing drive letters, G: that was mapped to a shared network location. This was confusing, because my G drive (4TB) suddenly became empty.
In CMD, type:
In Diskpart, type:
select volume 3 In my case, the drive I’m interested in is a Volume 3 – G drive.
The letter G has now been removed from the OEM partition. I was now able to map my network drive to letter G again.