OK, here's an update for this case:
TROUBLESHOOTING STEPS :
1. Suggested to copy the server private key backup from the old server so that it can be replaced it.
2. Imported the old server certificates.
3. None of the clients came online.
4. Used sylink replacer, and only able to fine only about 5 of the 40 clients
5. Suggested to use sylink drop
6. I used the silent switch on the sylink drop with GPO and updated 2 clients.
7. Confirmed that the clients are communicating with the manager.
RESOLUTION PROVIDED : Replaced Sylink on all the clients.