HRM Pro Plus - Weird Run Cadence

Hello,

I have a Garmin 965 which is working well for months and decided to add a HRM Pro Plus to better monitor the HR.

They are both paired with ANT+ and I am notified of the link when I start the activity.

But at the end the dynamics data are weird especially the run cadence see 

NB : I have already complained to the tech support and they have sent me a new one received today but same result so I guess there is no issue with the hardware

Is it a known issue ? Any workaround ?