I think the problem could lie with Polar. I have an M400 that will not accept a charge or get recognized by Polar in Polar Sync. finally gave up after fighting with it for over a year. Replaced multiple USB cords and sent the Polar back to them for repair under warranty.
Now have a Suunto ambit3 Peak and so far it works as advertised. (steep learning curve though)
Polar ought to get with the program and put our a product people don't have to struggle to get to work properly.