I reluctantly resigned myself to paying for a premium subscription to Endomondo for tracking my workouts with my Polar H7 heart monitor. Really wanted to use Polar’s Android apps (Beat and Flow)!! And I tried all kinds of things. But for getting data to My Fitness Pal and Google Fit — basically anything other than Polar Flow — Endomondo was the clear winner. And the only reason why I paid for the premium subscription is so that I could see historical data about my workouts.
Polar, if you’re going to have your own software, which it seems like you want to do despite having significant problems with stability and reliability, I suggest that you shore up the quality of your systems and software development practices. Otherwise, just stick to hardware and leave the software up to others.