You mentioned that talker as well as talker__rmw_connext_cpp failed with the same error. That implies that you have somehow disabled / removed FastRTPS from the build. Otherwise talker would be using FastRTPS. That difference could be related to the problem you are seeing and that’s why it is important to post the exact steps.
In step 3 you are running all tests on all packages. But the output you quoted is only the summary of the last processed package. For a summary across all packages you need to run ament test_results (optionally with --verbose).