Can you check if you get the black screens also with some other software-decoded videos (eg 1080p MPEG2 or VC-1 or by disabling MMAL acceleration in Player->Video)? Ideally with some publicly available sample file so it can be easily reproduced.
Would be interesting to know if it's a general issue with software decoded videos or if it's limited to Netflix, inputstream.adaptive or the widevine CDM.
so long,
Hias