When invoking an action, the controller waits on a promise of the result to complete in one of two ways: active ack (response from the invoker) or from the activations database. The latter is protected by a deployment flag and may not be enabled. However our tests did not test for both cases: with database polling and without.
I opened a PR to address this https://github.com/apache/openwhisk/pull/4623 As a side note, the PR also moves the time the controller waits before it terminates the HTTP response to a deployment configuration. This has the added benefit that some tests which took 1 minute each can now run with custom time limits (which I set to a few seconds). https://github.com/apache/openwhisk/pull/4623 -r