SNMP in Ubuntu times out with snmpwalk

I am trying to set up SNMP v3 network monitoring for Ubuntu either 18.04 or 20.04. I have loaded all the SNMP modules and configured a user and set up the firewall to allow 161 and 162. 'sudo ufw status verbose' shows ALLOW IN for ports 161 & 162. From this machine to a CentOS machine I can do an SNMP walk just fine. But from the CentOS machine to the Ubuntu machine it times out. I have used the exact same credentials on both machines. I even disabled AppArmor but no go.

Is there something I am missing? I am trying to use OpManager to monitor this and the tool gives errors as if I never configured SNMP.

...AR