Same here. All cores working like a charm except Mupen64. I’m running RA 1.3.1 (and tested latest nightly build with same result) in Shield TV (3.0 Marshmallow).
With RA 1.2.2 I had “RA stopped working” when I tried to load any N64 Rom. Now with 1.3.1 I can load but I get a black screen (and sometimes I can see the “Nintendo” logo or sounds).
Thanks for all you work.