I experienced multiple crashes with the Apple Watch app during my workout today. Specifically, the app crashed three times at different points, each time prematurely ending the workout.
I did not touch the watch or interact with it in any way to accidentally end it. Additionally, the "How hard was your workout?" prompt did not appear.
I am using an Apple Watch Series 5.
The app has crashed before, but very rarely, and always just once during the 'warmup phase' of the workout.