Hey,
After adding quite a lot of roms to my SD card RetroArch takes about 1-2 minutes to load. I get a black screen after the RetroNX splash. Also switching cores takes very long time. Have had it running for about one month without this issue with only snes and nes no-intro sets. It was after adding a bunch of mame, FBA, genesis roms that this started happening.
Cheers,