Apple Watch 5 calories are significantly different for the same workout

The calories are significantly different for the same workout. If I open a workout with the watch the calories are higher. If I don’t open a workout the calories are negligible. If I do a HIIT workout and start a workout with the watch, the calories will be, for example, 150 calories. If I wear the watch and do a workout without starting a workout on the watch, the calories will be about 30 calories. This has been frustrating me for sometime. Because it is so significant, I have a hard time trusting the accuracy of the watch. Is there a problem with the watch?

[Re-Titled by Moderator]