"Undo" workout doesn't work

I’m in the Zwift 101 Training Plan.
On a workout I accidently clicked on “I did it”. It added a green checkmark on the workout.
Then I tried to click “undo”, but it has no effect.

It’s not a big deal because I can find the workout in the workouts menu, but still looks like a bug…
And for other plans I’m not sure I can find all workouts individually, say in case I want to re-do a workout for example.