In case it helps, this is my experience with a SD2SNES rev E2.
I used 2 consoles to test and in both I had game crashes with Yoshis island:
PAL SNES with PAL/NTSC 50/60 hz : every rom from every regin crashes at intro before file selection
JAP NTSC SNES unmodified: only ntsc games are able to initiate playing (obviously) but with USA roms I can play until it crashes at first or second stage, but with jap 1.0 rom it does not crash.
I hope it helps.