RMI Connections error after NA upgrade

Hello,

After upgrading NA from 10.21 to 10.30 then 10.50 then 8.2018, I now facing the following error between my two HA cores, as some data don't reflect on both cores:

On Core1:
RMI Connections

RMI Error Local Core: rydnaap01 Remote Core: rydnaap02 Error: java.rmi.AccessException: SecurityException; nested exception is: javax.security.auth.login.LoginException: Missing or invalid security context.

On Core2:
RMI Connections
RMI Error Local Core: rydnaap02 Remote Core: rydnaap01 Error: java.rmi.AccessException: SecurityException; nested exception is: javax.security.auth.login.LoginException: Missing or invalid security context.

The two cores are up and running, reachable from each other, and I can telnet on port 1099, hostnames are resolvable, and core status shows as active-running in NA.

Please help