The recent 16MB (megabyte, not megabit) MegaDrive/Genesis game, Demons of Asteborg, fails to run via Retroarch.
Eke-Eke added support for SRAM in 8MB+ roms, despite using this updated core, content fails to run via Retroarch (failed to load content). Standalone SDL2 version runs the game just fine as do BizHawk.
You can grab the updated core and standalone version from here if needed https://mega.nz/folder/rgEVzAZK#uo-JSeS_abL94eE9xaNc6w