Hi lasdasdf,
thanks for the cross-link.
We are currently in contact with the vendor of the file system driver (Callback Technologies) that apparently causes VSS to break under certain mount conditions, we will let you know once we have a proper solution.
The current workaround is to enable Mount for all users
and Mount with Windows Mount Manager
in the advanced Boxcryptor settings.
Best regards,
Florian
PS: I changed the title since it is a general VSS compatibility issue, not only affecting Macrium Reflect backups.