Older Spektrum receivers are renowned for this type of brown out glitch. I have had experience of this and changed over to Sanwa/Airtronics and the problem went away after investing in new lipos, BEC caps etc etc. My advise is ditch the Spektrum and upgrade to a Sanwa/Airtonics, KO or Futaba and I think you'll find the problem goes away. It did for me.