Apple Watch series 4 - no longer tracking high intensity interval training active calories correctly

For the last week my Apple Watch has been incorrectly calculating active calories burned during my workouts. I used to burn almost 300 calories (with the same workout), that I am not only getting about 125 calories burned. I tracked this against a number of different workouts over the last week and the watch is calculating less than half of what it used to.

I tried everything - re-calibrated, checked allot he recommended settings, did an outdoor walk, etc. All software is up to date on both my iPhone and iWatch and this didnt help. I also force re-started both and this didnt fix the problem either. Please help.

[Re-Titled by Moderator]