This sounds like the same issue that someone else faced some time ago that I was unable to fix. :(
I don't think that I would be able to fix it as I have totally no clue, but I would still appreciate if you could share more information:
- Are you able to play other WebGL games?
- What kind of graphics card do you have?
- Is hardware acceleration enabled in your browser?
- Can you hear the BGM during the black screen?
Thanks, sorry for the inconvenience.