When I logged on tonight I was prompted to update Zwift PC client.
After the update no custom workouts are available. The workouts are all still in the correct file location on my laptop.
If I create a new custom workout it is placed in the same folder as all the other custom workouts and appears in Zwift. However, if I close zwift and then start it again the newly created custom workout is gone.
I tried rebooting laptop and logging out and back in to Zwift.