Sometime during AIX migration/alt_clone or HMC upgrade, it can happen that RMC ID get lost or duplicated, the the rsct process is unable to re stabilize the connection.
You can reset the key and restart that service as follows:
Reset RMC unique ID:
# /usr/sbin/rsct/bin/rmcctrl -z
# /usr/sbin/rsct/bin/rmcctrl -A
Then you can check the rmc status:
# /usr/sbin/rsct/bin/rmcdomainstatus -s ctrmc