There were really no weird intermediate steps (again: that I’m aware of). I just opened https://beta.observablehq.com/@fil/reprojecting-vector-tiles and it was broken (Chrome). I then tried to open it under a private window (still broken) and a secondary browser (Firefox) (still broken). Then created the demo from scratch to make sure it was not that code. (broken).
But hey! https://beta.observablehq.com/@fil/reprojecting-vector-tiles is still broken on my two browsers and on @clhenrick’s browser too 