If I click any draft notebook from https://beta.observablehq.com/notebooks, it quickly flashes on screen (apparently just fine) but the content is immediately replaced by a page stating “Sorry, we couldn’t find that page.”
Weirdly doesn’t seem to happen in Firefox, just Safari.
My workaround is to open the draft in firefox and either publish the notebook, or copy/paste everything into a new notebook in the original browser… yeah, not very satisfying. Fingers crossed for a quick fix from the observable team.