The detection of the FTP triggers only above a higher percentage of the maximum heart rate.

The following requirements must be met:

• Check if your maximum possible heart rate is too high. Your maximum possible heart rate must be set correctly in the capacity.
• The activity must be strenuous enough to achieve a high heart rate.
• The workout must have been performed with a heart rate monitor and power meter.

See: How can I determine my maximum heart rate from the records?