I found the same problem as well. I’m trying to get someone to fix it in ScummVM.
It is the plank walking death scene. I’ve played the Dos version of the game as well. There is no problem with the scene in Dos. ScummVM has allowed me to see the plank walking scene on the Apple IIgs version a few times, and there seems to be a problem with the this death scene.
When it’s actually worked on ScummVM (and not made the program crash), there are sometimes lines all over the screen, or lines in some parts of the screen, and there is no Captain. I think these colored lines might be the Captain, and that there is some kind of error in how they programmed him in the Apple IIgs version for that scene.
The only reason I say this is because the Captain is present in the Dos version of the game, and that is the only thing that is different, at least that I can see.