Forerunner 965 - Lactate Threshold not Updating - 21.19

I have a Forerunner 965 running Software Update 21.19. The last time I received a Lactate Threshold update was the 4th November despite having completed 14 runs since this date of various types / intensities (Threshold, Sprint, Easy). Prior to the 4th November my Lactate Threshold was updating regularly. I always run with a Heartrate Monitor (HRM Run). I have Auto Detection switched on for Max HR, Threshold and FTP. 

Is there another setting that I am missing?