HRM 600 Running stats - Wrong stride length (outdoor run)

Hello.
I am using HRM 600 in a pair with phone app Garmin connect. No watches. When I start run I start Activity recording and then sync its results to Garmin app to have there running statistic.

My problem is that HRM 600 incorrectly measures stride length and as a result - total distance has 20% mistake (1.2 km instead 1km.) I set custom stride length in Garmin connect but it is ignored in calculations.

May anyone help me to find solution? Thanks and BR.