If you you have your TP workout plan in HR zones it may not work (like my case and many cases in here), I change specific workout in TP from HR to Power and it worked! Now I can see it in Zwift.
The way to do that it is shown in this video in Youtube: " How to Change Workouts from Power to Heart Rate in TrainingPeaks" (it changes from Power to HR instead, but the steps are the same to change it the opposite way):
Another important thing to mention is that Zwift will only show the workout scheduled on that day in Training Peaks, so make sure you are matching it (or moving it to the appropriate date) in Training Peaks Calendar.
Hope this helps.