BMR can fluctuate, it depends on many factors, such as your daily activities, the food you ate (if you had a lot of protein food it may cause a sharp change of BMR), even the outside temperatures may affect it.
It also depends on how many hours a day you wear your GoBe2. If you wore it only for a few hours on one day and then the whole day the next day, your measurements will be different. To get the most accurate results, we recommend wearing GoBe2 all the time and taking it off only for charging.