The SSL stack is improperly setting an If-Modified-Since header on the CRL request EVEN THOUGH it has just determined that it does not have this content in its cache.

    https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/304

The HTTP 304 Not Modified client redirection response code indicates that there is no need to retransmit the requested resources. It is an implicit redirection to a cached resource. This happens when the request method is safe, like a GET or a HEAD request, or when the request is conditional and uses a If-None-Match or a If-Modified-Since header.