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