So I've had my Osmo mobile a couple of weeks. Barely used it as have been away with work. Have gone to it today and had a play, and whilst filming the gimbal just cut out. Turned it off and on again and the gimbal worked until I reconnected the app to the handle then it went limp.

I've deleted the app and re-paired the gimbal to the phone and there's no improvement.

The gimbal works for about 5 seconds before the yellow light starts flashing and it goes limp again. The phone is properly balanced and this thing has had barely any use. I've tried two different, fully charged batteries in it.

Any suggestions before it goes back?

Think I've solved it. Seems that although the Osmo mobile didn't mind my iPhone 7 in a black case last week, this week its decided that it doesn't want to work with it.
I have solved the issue with an elegant solution - a piece of post-it note over the phone sensor.

Thank you for this. I just experienced the same situation. Totally unaware of the consequences I've put such slim, black cover on my iPhone thinking it would be better for protection as my original, quite thick and heavy one did not work with the gimbal. Next day went shooting and the phone was constantly loosing connection with the gimbal. It was lottery - was working couple of minutes and than the gimbal was disconnecting. Was ready to send it back and found your post. Removed the cover and guess what ;) No disconnection since. Not even one. What a crazy issue! So what if someone has the black phone? (mine is gold iPhone luckily)..