The page is served with its own copy of Scalar and of the API document, so this is not a network problem with anything third-party. Reloading usually clears it.
The document itself is always available as openapi.json — it is the same file the reference reads, generated by the daemon being released.
If reloading does not help, the browser console will name the request
that failed: either ../generated/scalar.js or
../generated/openapi.json.