Hello! Sorry to hear that you are having some issues (and that you were sick, hopefully you are feeling better!). Can you try downloading the latest version, v0.4.0.6, and see if the black screen still occurs? I think there was a bug fix not too long ago related to that.
The Load Map issue might be something different, but not sure off the top of my head. Let me know after exporting with the latest version if you still have either of these issues. Also, if you are okay with downloading the Itch desktop app, I'd recommend doing so. It's a pretty cool app and it will automatically keep RPG in a Box up to date as I release new versions of it.
I hope you are having fun with it so far! :)