This is apparently a known bug when using a combination of VMware UEM and VMware App Vols 2.11. If you capture Office 2013 or 2016 you may see the following error:
In my case it created a mount point in a hidden folder called SnapVolumeTemp on the root of C:\
Locate a file called allvolattached_shellstarted.bat and edit it. Note the ‘a’ specified as an argument for FlexEngine. Remove the ‘a’ and save the file.
Detach the disk and test again on VDI desktop. The error should have cleared at login.