I have a Fenix7X and the training effect is often overestimated. Today I had an easy long run, always staying within Z1-Z2, and it calculated "Tempo" as primary benefit. Based on other threads it's a common issue, and in some models it should be fixed, but it's definitely a miss on my watch. It's not fixed in connect as it was for others.
My SW version is 11.28. I recently updated my HR zones, and I wonder if for any reason the watch still did the calculation on the old one.