I'm glad you are enjoying the game.
The issue seems to be related to the game failing to load an image from the server (!$soul-door-progress.png is art used in the second dungeon).
I'd guess that the browser cached a broken version of the image, and you finally got it to load it again correctly after resetting the computer.
If this happens next time, try reloading the page doing "Ctrl+F5" or "Shift+Ctrl+F5", those commands should force the browser to load the cached images again.