Synology issues with Active Directory

q: A customer called today about their Synology.  It seems they can no longer authenticate to the shared folders using active directory credentials.
a: After a reboot didn't fix it, we reviewed the Domain/LDAP settings in Control Panel.  It seems a recent update may have changed some of the settings.

1. They are running DSM 5.2-5565 Update 1
2. We checked the box "Advanced domain options (Required only under specific network environment)." 
3. Then we stepped through the wizard of joining the Synology to the domain again.
4. For Domain NetBIOS name, we used the NetBIOS name of our domain (the domain without the .local in most cases).
5. For Domain FQDN, we used the full domain name (including the .local or other suffix).
6. For Update user/group list: we set this to Daily and Every 12 hours because their AD structure does not change that frequently. 
7. After that completed, drive mapping worked again.