Well, I took another look at migrating to Seafile 11 Pro.
After dealing with the bug related to the LDAP_SYNC_GROUP_AS_DEPARTMENT option.
I finally figured out why my LDAP groups were staying desperately empty and it was just by pure chance.
It turns out the issue was with the LDAP_USE_GROUP_MEMBER_RANGE_QUERY option for group syncing.
Once I set it to false, the groups populated normally. It took some time to figure it out. Lucky