If you see your mapped drives disappear you may have a Group Policy that maps your network shares using the REPLACE feature. Another symptom I noticed occurs if you remote (RDP) to a different PC and leave it for a few days, multiple mappings for the same letter will appear.
The simple fix is to set the Drive Map GPO to use the Action UPDATE.
To stop your mapped drives disappearing or automatically closing:
- Launch Group Policy Management
- Find your drive mapping GPO, right click on it and select EDIT
- Expand USER CONFIGURATION > PREFERENCES > WINDOWS SETTINGS > DRIVE MAPS
- Double click on the drive map that is automatically closing
- Change the ACTION drop down from REPLACE to UPDATE
I found this problem occurs on Windows 10, but others have found it on many older operating systems.
If this does not solve your issue, you might find this discussion on the Spiceworks blog to be helpful.