My Fitbit Charge 5 Turnsoff during HIIT Workout

[Haru000]

My charge 5 lately turnsoff during my High Intensive workout when my heart rate becomes really high.  Never had this issue before. Not sure what's going on now.  Hate losing those stats.

[Mordaw]

My Fitbit charge 5 did exactly the same thing tonight after I had done a hiit step class. It monitored the class then turned itself off. The battery was showing in my app as 95% but I couldn't get it to sync either then when I eventually managed to figure out how to restart my charge 5 using rhe charging cable it synced then rhe battery was showing as 68% and there was a red light at the back of the fitbit flashing red. 

[Haru000]

Have the same issue.  After I'm done with my workout, I charge my chrge 5 and it would turn back on, but it normally took some time before I can sync it. Of course, it did not capture all the data for my workouts. For the past few mornings,  I actually monitored my charge 5 while doing HIIT.  Charge 5 would turned off when my heart rate went over 180/min.  As I said, I never had this issue before since I have been doing the same HIIT workouts every morning.  My charge 5 is only about 2 years old and this is the third Fitbit watch I have been wearing.  thinking of changing to Apple watch for my next one.