iPhones cannot communicate with Windows PC via USB connection - no images are shown

Hi Community, 

I got several iPhones (DEP) managed in Sophos Central and none of them can get communicate via USB as they are connected to the PC. The iPhone itself gets displayed in the windows explorer. But there is no further folder DCIM or any images, that are stored on the iPhone. So I guess it must have something to do with Sophos Central. I checked all points but I could not solve the problem. I also enabled "USB-Pairing" option in Apple DEP settings area. But it still does not worked. 

This behaviour only ocurres on Apple DEP devices. On other Apple devices that are not DEP distributed and therefore not fully managed ths problem is not ocurring. 

Any hints on that? 

Thanks in advance!

Marcus