My wife and I both have Aftershokz Trekz headphones (Air and Titanium models respectivly) and in the last few days we have noticed that the headphone button is not working as it used to pausing/skipping songs. It still works on other audio apps.
This seems to be an ongoing issue forthe android platform and it is currently under investigation. You can track it and read more about it here. Also don't forget to vote for it. Hope this gets fixed soon 🙂