I like the first level being hard !
But I had an issue with the door not loading because I was having a portal from last stone to it, and it made me restart before I understand this issue, or maybe it's on purpose that we need to walk to it (I solved it by putting a dummy portal further the door). This happened to me on level 5 too.
Or sometimes I would get stuck on a corner walking (but I don't think it's an intended bug haha)
Nice game overall, it might be hard as a start (but I like it), sometimes it's not clear in terms of feedback why a portal doesn't "click" and disappear, and yeah this door thing.
It's original but it looks like different solutions should be tested more for a level.
Great game for a game jam though, I'm just saying all this because I read you planned to release it on mobile haha