steps not being tracked as exercise session

[Cochise]

Have used my Charge 2 (and earlier Fitbit trackers) for about 5 years.  This week I developed an unprecedented problem.  Even though the device does count my steps and it does reflect my walking as active minutes, it does *not* reflect the walking as an exercise session.  Over the years, any 10+ minutes of walking would count as an exercise session.  I have not changed any settings.  But, suddenly this week, not even 25 minutes of walking will result in an exercise session being recorded.  I will appreciate any advice on possible remedies.

[Rich_Laue]

Are you letting Fitbit decide or using the manual mode. 

Are you taking any prolong rest stops? 

[Cochise]

Thank you, Rich_Laue. 

When I log an exercise session manually, it works just fine.  But, if I let Fitbit decide, then no exercise session gets logged, even though the steps are tracked, and active minutes are recorded.  It has happened three times this week.

And, no.  I have not taken prolonged rest stops.  (Good question, though.  I appreciate your thinking of it.)