There are definitely issues with the D50 line-in (and so perhaps with the mic-in as well) with Neutrik right-angle plugs. You can reproduce the drop-out by putting pressure on the input plug, if this is your problem. I ended up ditching my SP cables and getting Vark Audio to make me ones with Neutrik on one end (for my MMA6000) and Switchcraft on the D50 side.
Vark cables also solved an issue with my MiniR84 giving me rare random digiglitches (maybe once/twice per hour), I swear by these guys.
Jeff