We just updated to 11.5.1.2266, restarted server, then the default group kept repopulating with disconnected computers which were listed as been connected in different containing folders.
Fix
Make a note of the ones that keep repopulating in default.
Disconnect ghost service, right click in the system tray “Stop Symantec ghost config server”
Delete the noted entries in default
“Start Symantec ghost config server”
Go tools remote client install
Reinstall agent to the noted computers that keep repopulating
We had to repeat the steps a couple of times to get them all, but it worked.
Hope helps Leon