I figured out the disappearing PWP glitch! To make it appear, just start a new pwp with Isabelle, and enter a building. The pwp that you seeded should be there, and the roped-off section should be gone.
yeah I figured this out a while ago, but it doesn't really help. I mean, the PWP you've just started will become invisible also...
If you cancel it then the previous PWP will go back to being invisible. I think the only way to prevent this is by sacrificing 2 pwps