Select a client from default group or other group, select command Move from the right click context menu. Select the desired Active Directory group (default name is Users), it action will result in a popup error.
The client cannot be moved to the Active Directory group.
This is working as designed. It is forbidden to move client to AD group from other group in SEPM. These clients presented in the SEPM console are imported from Windows server AD/LDAP.
All modifications needs to be performed on the AD then resynchronize.
If clients show up in Default group instead of AD group after import from OU, it might not be in sync with the AD server. Synchronize it by clicking the AD group name and select Sync Now.