"An investment of a couple of dollars from Amazon or Ebay will gain you what's known as a 'pry tool' used in mobile phone repair. Just google 'mobile pry tool' and you'll find plenty of examples. They look like this:
"It's really strange that it happens immediately for you but not for 3DR when they tested.
Out of interest, did you ship the LIPO with the Pixhawk/motor/ESC? I'm wondering if there's some strange voltage sag that happens when you flatten the…"
"It certainly sounds like a Sync issue to me. EG: https://www.youtube.com/watch?v=5pBdDMxWsgs
You absolutely should have signal and ground wires attached to your APM/Pixhawk.. Leave any BEC power disabled until you've sorted the issue."