Fitness App counts way too many calories (approx double) - used with a Garmin Watch

Hello

Since I did the last iOS update, I have been able to use the Apple Fitness App, although I do not have an Apple Watch. I have a Garmin Venu and use Garmin Connect as my main way of tracking activities, however I enjoy the extra data that Apple Fitness gives so I've been using it too.

Unfortunately, the app is way off when it counts my active calories on my Move Circle. I believe the issue is that my active calories are counted twice, once by Garmin, once by my phone. The settings are set in a way that the app should take data from either one device or the other, but the fact that the burned calories are off by being almost double of the real each time leads me to believe it's a matter of the two devices competing with each other.

Does anybody have a solution? Is it a software integration issue, or can I do something about it?

Before you suggest it, I would rather not have my Fitness app solely taking the data from my phone, or from my watch, into account. I don't have both devices on me at all time and I like that the app is - supposedly - switching between both.

Thanks in advance for your help.