Unable to re-register client

We just migrated our Avamar to a new hardware and upgraded from 7.2 to 7.3. All seems working fine except for 3 clients suddenly become offline. I tried to re-register the client but it failed. Here is the error message

2018-05-24 21:38:16 avagent Error <18931>: Registration: Unable to send the certificate signing request to the MC.

2018-05-24 21:38:16 avagent Info <18936>: Unable to securely register with the MCS (xxxxxx)

2018-05-24 21:38:16 avagent Info <5321>: Unable to connect to Management Console (xxxxxx), sleep 24 minutes, 28 seconds before retry

2018-05-24 21:41:34 avagent Info <5705>: Updating IP address with the MCS. local IP='172.18.253.171', registered IP='(none)', port changed:false

2018-05-24 21:41:34 avagent Info <18918>: Registration: Processing secure registration with the MCS.

2018-05-24 21:41:34 avagent Info <18921>: Registration: Requesting root CA from the MCS.

2018-05-24 21:41:34 avagent Info <18926>: Registration: Saving root CA.

2018-05-24 21:41:34 avagent Info <18928>: Registration: Creating certificate signing request.

2018-05-24 21:41:35 avagent Info <18930>: Registration: Sending the certificate signing request to the MCS.

2018-05-24 21:41:56 avagent Error <5365>: Cannot connect to 1xx.xx.xx.xx.xx0:30003.

2018-05-24 21:41:56 avagent Info <5059>: unable to connect, sleep(60) then retrying

2018-05-24 21:43:17 avagent Error <5365>: Cannot connect to 1xx.xx.xx.xx:30003.

2018-05-24 21:43:17 avagent Info <5059>: unable to connect, sleep(60) then retrying

2018-05-24 21:44:38 avagent Error <5365>: Cannot connect to 1xx.xx.xx.xx.xx0:30003.

2018-05-24 21:44:38 avagent Info <5059>: unable to connect, sleep(60) then retrying

2018-05-24 21:45:59 avagent Error <5365>: Cannot connect to 1xx.xx.xx.xx.xx0:30003.

2018-05-24 21:45:59 avagent Info <5059>: unable to connect, sleep(60) then retrying

2018-05-24 21:47:20 avagent Error <5365>: Cannot connect to 1xx.xx.xx.xx.xx0:30003.

2018-05-24 21:47:20 avagent Info <5059>: unable to connect, sleep(60) then retrying

2018-05-24 21:48:41 avagent Error <5365>: Cannot connect to 1xx.xx.xx.xx.xx0:30003.

I can telnet to port 28001 from client to Avamar server but not to port 30003. Checked with our local network there's no firewall rule on port 30003 and it should not be firewall issue since other clients on the same network are working fine.

Anyone have the same issue before?