The same problem reported long time ago as https://forums.garmin.com/apps-software/mobile-apps-web/f/garmin-connect-mobile-ios/273874/garmin-connect-workout-graphs-missing-goal-pace-heart-rate-target-lines-now seems to be back again in GCM 4.70.1.4:
As shown above, the Power Target white line is flat at 0.
It should look like
Can you see the same in your workouts?
Thank you,
Jarek