garmin and health app sync incorrect

I use a Garmin watch to run with and in the health app I have the Garmin connect app set to "allow to write" for Walking + Running Distance. When I look at the distance in the health app it is never correct. For example this morning I went on a 3.5 mile run using the Garmin watch and then I went on a 1 mile cool down walk using my Apple watch. So I would think I would have a minimum of 4.5 miles showing in the health app but when I looked it said 4.2. It also happens with Cycling mileage from Garmin connect. I rode the stationary bike for 4.71 miles and entered that into Garmin Connect. The health app only showed 1.8 miles. I reached out to Garmin and they said it is a health app issue. Any help would be appreciated.