Zwift crashes during workouts

after using Zwift for a long time without problems I had it crashing today.
I started a workout and after approx. 45 minutes the application just disappeared from the screen. Other software like Spotify continued working.
I restarted Zwift and began the workout again. Now it crashed after only 10 minutes. Again the entire program was gone. I restarted again and just did a ride - no workout. In this mode I could train for 45 minutes without problems. I did not restart Windows, I don’t think it’s the PC that causes the problem.

My system is a Windows PC, the Tacx trainer is linked via ANT+. Any ideas?