We've got trouble with different cache headers for the same page request. Sometimes we saw the correct no-cache headers and sometimes the default cache configuration headers.

The pattern is that every first request after a cache flush will use the configured browser cache policies and overwrite the cache headers set by code. See Cache header negotiation

The reason seems to be that missing cache entries will be stored as uncacheable cache entries in the cache. And then the cache will bypass such cache entry requests. But for the first request the browser cache policies will overwrite the existing cache headers.