Pool & members showing up in active LB but in standby it is showing down.

Hi, 
This is not a Sync problem or in other words ( HA doesn't Sync Pool members Status ) as the standby unit should do the health monitoring by it's own selfip ( specially the selfip that can reach to servers/pool members ) 
so in this case you need to do the following: 

1. use #ip route get <Pool_member_ip> to know which selfip in the standby unit reach/talk to servers.
2. If you have a Firewall between your Bigip and servers , you need to monitor if the standby selfip sends health monitor packets periodically to servers or not, also you need to check if the firewall allows the access between the standby unit and servers.
3. Try to perform telnet test on LDAP port and see if you can connect or not.
4. Take a packet capture for health monitor traffic between Standby selfip and server, Packet capture should show you what is the issue exactly in the standby path to LDAP servers. 
5. Please check this article , it has more insights for health monitor troubleshooting and a sample Packet capture command: 
   https://my.f5.com/manage/s/article/K12531