You could try to investigate with a Before profile archive import Logon Task, running something like cmd.exe /c DIR H:\ >"%USERPROFILE%\H-DIR.txt". Maybe it shows something that helps find the culprit. (Be sure to configure a timeout so it does not cause your logon to hang .)
If it works post-logon, you could work around this by using the Disable DEM Drive Mappings during logon policy setting from the advanced ADMX template (or the NoAD equivalent equivalent UEMActionDriveMappingDuringLogon="0") and launching a drive mapping refresh at a later stage.
DEMdev Thanks for your tip!
I used your tip to find the culprit and when looking at the created .txt file i saw the following:
Volume in drive H is CVApps
Volume Serial Number is AEE0-8B16
Directory of H:\
04-09-2019 00:48 0 allvolattached.bat
04-09-2019 00:48 1.355 allvolattached_shellstarted.bat
04-09-2019 00:48 320 cache.dat.initial
20-01-2020 14:19 1.472 cv_prestartup.log
20-01-2020 14:20 408 cv_prov_post.log
20-01-2020 14:20 6.225 META.ZIP
20-01-2020 14:20 <DIR> METADATA
20-01-2020 14:19 <DIR> OfficeTokensBefore
04-09-2019 00:48 261 prestartup.bat
04-09-2019 00:48 7.043 prov_post.bat
04-09-2019 00:48 372 shellstart.bat
20-01-2020 14:22 24.349 snapvol.cfg
04-09-2019 00:48 0 startup.bat
04-09-2019 00:48 384 startup_postsvc.bat
28-08-2019 02:12 102.640 svoffice.exe
28-08-2019 02:09 228 svoffice.exe.config
04-09-2019 00:48 16.452 tokens.dat.initial
04-09-2019 00:49 20 version.txt
28-08-2019 02:12 87 VERSION32.txt
28-08-2019 02:17 87 VERSION64.txt
18 File(s) 161.703 bytes
2 Dir(s) 21.300.944.896 bytes free
To me it looks like an appstack or writable is attached before login and is using drive letter H: and a bit further in the process the driveletter is released as it is not visible afer login.
We do use Writable Volumes and Appstacks so that makes sense, but i never had any issues with driveletters before.
Do you have any idea what could be te cause of this?
These are the registry settings on HKLM\SYSTEM\CurrentControlSet\Services\svservice\Parameters
Is that H: drive maybe just hidden from File Explorer? That is, can you still DIR it from a command prompt within the session?
W.r.t. why you did not encounter this before, I guess you're better off in the App Volumes forum. I'm DEMdev, sorry .