Is the user validated, everything looks OK, but the drive does not mount?

Usually, this is because the client is started with administrator rights.

Do not do this. The client will start under different credentials than the user, and due to security, the drive will NOT mount correctly.

If so, right-click on the icon, select "properties", and click on the "compatibility" tab.

In the compatibility tab, make sure that the "Run this program as an administrator" option is unchecked.

Afterwards, click on "Change settings for all users", and make sure that the "Run this program as administrator" option is unchecked here as well.