calories at rest

Nobody??? Did the resting calories stay the same or did they decrease by about 200 calories comw on Instinct 2? 

Did you change your wearing habits? Wearing while sleeping, etc.? The algorithm is based on the HR, HRV, respiratory rate, etc.

Burned Calories Calculated on My Garmin Device Are Wrong

And possibly related to this since you recently updated - Resting calories randomly dropped

then the update is only on the instinct 2!! but why do it only on one device? also because it improves the accuracy 

2836989 said:

then the update is only on the instinct 2!! but why do it only on one device? also because it improves the accuracy 

I do not know whether the algorithm for Resting Calories changed on other models, but the value on my Instinct 2 is rather close to the value as calculated by the RMR online calculator at RMR Calculator | Resting Metabolic Rate Calculator (omnicalculator.com). When entering the same data into the calculator, as I have in my Garmin Connect profile, the calculator shows a value ~70 Calories higher than Garmin Connect. Before the Instinct 2 firmware adjustment, Garmin value was more than ~130 Calories higher than at the calculator.

Most other online calculators show significantly lower value than Garmin. This one was always the one the closest to the values from Garmin.

So if you test the calculator with your data, and get a slightly higher value on the calculator than in Garmin Connect, then your watch probably uses the same algorithm as Instinct 2. If the result from the calculator is quite a bit lower than at Garmin, then your watch probably uses the older algorithm with ~200 Resting Calories more.