Someone else with a digital download version (Impulse) ran into a similar problem recently:
Cannot open chests. In that case, they could not pick up items, take stairs, etc, if they were in the vicinity of the warrior's guild in the Dark Forest. Their save was not corrupt, though, and worked fine loaded in the CD version (1.0034A) of the game.
Shunmaha's crash problem with Shrimpo was also absent on my system, but from the description appeared to be triggered when Shrimpo attempted to heal himself (either the character animation when he turned around, or the spell effect).
I suggested a clean re-install of the game, but did not hear back about any results.
Interestingly, the imp castle and the warrior's guild are the only locations on mountains, though that may just be coincidence.
There is a file verification procedure in the topic below, though it is for the CD version of the game, and I'm not sure how many game files were changed between that and the GOG version. If a clean reinstall doesn't fix your problems, though, it could possibly be helpful.
Troubleshooting Tips (& manual install procedure)I assume you tried various compatibility mode options, etc?
