We have found IBM i ActiveGate extension see only 1 service instance running on the server but that host is running 2 services instance, 1st one running on port 443 and 2nd running on port 8080 the Dynatrace showing only 443. The Dynatrace can't monitor 2 instance on same server ?
Do you mean the Service entity like this?
If this is your issue, then you don't have any transactions monitored by OneAgent (on systems) which make requests to that port 8443. Those service entities for extensions are in fact opaque services detected by OneAgents from applications calling them.