On my most recent RotDG game I had run into an issue where I had entered a mysterious portal on the 9th floor. Inside the special stage (floor 0) there was another portal (usually to exit back to the plane you were on before) but instead sent me to another floor 0 (different layout and texture theme) but when I got to the end of that one, the mysterious portal sent me back to the previous floor 0, in which there was no other way out. I'm assuming that multiple layers of special stages wasn't intended (lol makes me think of inception) so just be on the lookout for this problem and avoid mysterious portals on much deeper levels to avoid losing all progress.
Don't kill me for this, but "Yo Dawg, I heard you like Mysterious portals, so I put a mysterious portal in your mysterious portal so you can explore mysterious portals while you explore mysterious portals." I'm sorry, I really am, but I had to. Just once.
