1529 is pretty low. Did you do the type 2 bcg mod?
When you say double feed, that makes me think mag issue, as in spread feed lips but if it's across multiple mags and manufacturers probably not the case.
Previous round not ejecting all the way? two fresh rounds stuck? Stove pipe? What's ejection like? Lock back on the last round? Have you messed with the gas setting(any change in operation, ejection pattern/ distance)? Which deflector installed?