This means that pins are shared between 262/402/etc and also between the draft spec and PR previews (everything on tc39.es). The observed behaviour is that every time you load a document on this domain, it clears any pins for sections that that document doesn't have. Which is often the case for PRs that add sections (you will often pin the added section) or when switching between 262 and one of the other specs (all pins are cleared).
This means that pins are shared between 262/402/etc and also between the draft spec and PR previews (everything on tc39.es). The observed behaviour is that every time you load a document on this domain, it clears any pins for sections that that document doesn't have. Which is often the case for PRs that add sections (you will often pin the added section) or when switching between 262 and one of the other specs (all pins are cleared).