What do HTTP errors and timeouts mean?

A 403 may indicate blocked automated requests; 404 means the page was not found; 429 usually means too many requests; 5xx responses indicate a server problem. Pages taking more than 15 seconds or exceeding the 2 MB HTML limit are rejected by the proxy. Non-HTML responses are skipped too. Review your own site configuration or try later; do not bypass access controls.

The feed reports the URL and the reason it was skipped. If the first page fails, the crawl stops. If later individual pages fail, eligible results can still be exported as partial results.