When you sign up for a Stryd training plan within the Stryd system, your calendar will be populated with all your future workouts. When you look at the workout in the Stryd mobile app, the Stryd system can predict the length of each time-based workout.
If you sign up for a Stryd training plan before there is enough data in the system to make a time prediction, none of the future workouts have an estimated distance. This will not change even if you have more runs in the system and the Race Power Calculator can predict race times.
The workaround is to add the training plan again once the Race Power Calculator can predict race times (typically after about 5 runs in the system). If you select the same plan and race day, the workouts should be the same (you can then remove the plan added previously)