It look like this is a bug by the LDMS10 upgrade. The problem is also descripted here by Landesk Devices are not showing up in their appropriate Active Directory Organizational Units under scope properties
I´ve installed the LD2016-SU_BASE-2016-0301 patch cause of other problem I had with LDMS10, but the patch don´t help me with this issue.
I found out a workaround: In the window "Select visible devices..." click on "Browse directories" and now you see the entire AD-tree. Right-click on one OU let´s you create a new scope of this OU and the newly created scope in fact lists up all computerobjects found in that OU.