Last fpv flight of the day

Last flight of the day flew 7 lipos today with my rebuilt qav r. It had started to flip and fall out of the sky randomly and on the third time decided to strip it down completely and do a rebuild. only thing I found suspect was a broken nylon standoff under the pdb and lots of dust on the pdb and the underside of the fc!! cleaned it all out and so far no more death flips thankfully