SDL2 still has a few bugs, particularly with memory handling. I've been testing a number of games, and on my machine (MacBook Pro running 10.13.5), the screen fails to update in most games until I move the mouse around a lot. In certain cases, like Warcraft II, everything plays fine at first but always crashes after a few minutes with a malloc free error.
It probably will take some time and familiarity with SDL2 to debug, but my preliminary tests have found that it is always a double free or freeing a non-existent pointer error. The two places where it can happen are calls to SDL functions: SDL_BlitSurface on line 878 of video_sdl2.cpp and SDL_SetSurfacePalette on line 1083 of video_sdl2.cpp.
Maybe it's just me encountering this problem, but I'll try to debug further anyways.
Thanks to all the contributors and maintainers for keeping SheepShaver alive
