There seems to be a defect in Garmin Connect mobile app for Android version 4.25.2. When I view an activity based on a structured workout with heart rate targets the Heart Rate (bpm) chart target line is displayed for only the first few minutes. The defect appears to only impact the mobile app; on the Garmin Connect web site the target is correctly displayed for the entire activity.
For example today I did a 9 mile run with a structured workout. On the Heart Rate (bpm) chart the target line is only displayed for about the first 5 minutes of the activity. The target values are correct but it seems to be compressed into the beginning of the activity and then it just stops.