A recent Windows 10 update changed the SMB discovery method to one that isn’t supported by MyCloud (or many other NAS). I’d check your Windows versions; I suspect the one that is working either hasn’t updated, or is using the old mappings.
You should be able to examine to drive mappings in the computer that still has access, and enter the path manually when you map network drives on the other computers. Make sure you enter the same MyCloud user credentials for every share you map (another common Windows gotcha).
Search the forum for the discovery problem. e.g.
