Hello, @Szymon Rabiza and all.
Further to the archived thread at <https://social.technet.microsoft.com/Forums/en-US/f4460a73-6a42-47f8-950b-2f18e03c0a7e/impossible-to-remove-a-persistent-network-drive-mapping-when-logged-on-disconnected?forum=win10itprogeneral> and the above answers; you may wish to use the following commands.
Net Use z: /Delete
Mountvol z: /d
if not exist z:\ (Net Use z: \servername\share /Persistent:YES)
These three lines can be concatenated into a single command line expression, by using ampersands (&).
I have struggled for the last six months and have developed an elaborate batch file to remap my home network drives on my laptop; as Windows 10 doesn't always find them again. Today, the referenced archived thread pointed me to using both Net Use /d and Mountvol /d — as a pair. Kudos to @Giacomo and @Grajon, as the net use and mountvol pair obviates the need to stop and restart file Explorer; which itself introduces other (potential) issues!
PS. Per the original/archived thread, I too suspect this is an unresolved Windows 10 bug.