You probably should analyze this with a Pega trace. In general, if the harness is failing to be found, it is because the class of the harness is not an inherited class of that of the step page, which in turn might be missing, which in turn might be because the thread or requestor is gone.
The CPMInteractionPortal harness is in class CPM-Portal, so you are looking in the correct place for it. Have you confirmed that the harness does exist? Have you examined your ruleset stack and confirmed that you have access to the ruleset/rulset version in which this harness lives? If neither of these two simple checks turns up the source of the problem, then you should run with the Tracer to see what is failing. Make sure to select all event types and all rulesets so that the Tracer does not omit some critical fact.
You should also be aware that this rule is Circumstanced. There is another version of this rule that is used when CPMPortalType is equal to "CPMInteractionMobilePortal". If you are running with the Tracer, you should see what is the value of CPMPortalType. Perhaps you are looking for this alternate version of the harness, and you don't have access to it.