On PC I'm using the latest nightly, and Sega CD with bin+cue works fine there so the issue itself still must be port specific.
So, 1.5.0 works on my Wii U no problem, game loads just fine, all set.
Just in case this is related: The way I load homebrew is pretty standard I think as well, I just boot my Wii U up, CBHC takes over and boots me into the Wii U menu, and I load "Homebrew Launcher" from the icon on my Wii U menu- I've of course been using retroarch_rpx
downloads since rpx is supposedly better (at least from what I've heard)
Anyway, I just tried 1.6.4 per both of your recommendation with a default configuration, and I'm getting a "DSI: Instr at 0D11C368 bad read from unmapped memory" followed by a bunch of addresses- it looks like it may be related to
this issue on github for me, as every time I get a crash it's always a similar error.
One of the things I tried was setting the menu driver back to rgui, just in case the assets being loaded was causing the crash, but instead of crashing, I just get "failed to load content" error- unless I need to switch to the Genesis Plus GX core from another core, in which case I get that "DSI: Instr..." error again.