Ok, I gave the game a second chance. I actually ran into the bug again, but it made it clear what the issue was. It was actually losing the fight against the snakes that caused the issue. If you lose a fight, retry from the main menu (which places you back at the same fight) and continue on, then the final boss doesn't properly appear (instead going to the credits). Weird issue, but once I figured that out, I just had to get good and not lose to the snakes.
It's a really good game. I was very happy to actually see the story wrapped up. The balancing seems a little off, with luck being often the single deciding factor to a fight. Also, I feel like the fire dice are really under-powered, since every other dice gives better effects while also allowing for larger rolls. If the fire die only used one energy block total instead of one energy per rolled dice, maybe it would be more effective.
Either way, I'm glad I gave it a second chance. I updated my rating based on my most recent pass through the game.