Ok, I understand. Is there any technical information I can pass over to them? I do not have any difficulties with “in deep” and “programmer-like” explanations as I a do backend development myself but never confronted with contact/account management under android. I will then pass that information over to blackberry to let this issue be fixed.

Hello, Do you think this is a DAVdroid problem? Did yoo already contact Blackberry support about that?

We got a message from another user using the Blackberry Hub who found the solution: In the Blackberry contacts app in the preferences check all accounts (also accounts that don’t have any address books). As a server the reporting user is using a mac OSX. Thank you!