Polar H9 heart rate monitor problem

Hi all,
I have just started using a Polar H9 heart rate monitor for running. For some reason the apps (polar beat/flow) stopped recording 3 times after exactly 7 minutes. I tried it on a hike and it worked fine. Has anybody else had similar issues or have any suggestions to resolve it. I contacted Polar who advised a couple of things that haven’t worked.
Thanks in advance