UPDATE FROM STRAVA:
Hello all! We are going to mark this Known Issue as resolved. As of now, Peloton is working on the issue and if any athlete's are having repeated issues, please reach out to Peloton for updates/troubleshooting (https://support.onepeloton.com/). In the meantime, the workaround would be to enter the missed activity manually on Strava to get the credit for the missing activities.
Not sure where to report this - I put a note up on Reddit and I'm not the only one having this issue. If you use the Peloton App (I was traveling and using at a Hotel Gym) any classes will usually sync with Strava - for some reason any of the Walk/Run classes will no longer sync to Strava. You can take a cycling class, a yoga class, a stretch class, anything else - they all sync fine, but the Run/Walk classes no longer sync.