Fictioneer 5.18.2 (Hotfix)
Hotfix: The majority of cache plugins should now really be compatible with the Post Unlock feature
For those who are interested as to why this did not work: Cache plugins worth their bytes do not cache posts that are password protected, for obvious reasons. Some try to be smart about having multiple versions of the page, though.
Anyway, due to the password bypass, the plugins did no longer know that the post was protected. Because instead of checking for the presence of a password, they only check whether the post is protected for that request -- which it might not. So if someone had the post unlocked, the plugin would cache the page like any non-protected page and serve it to everyone. Great. Wonderful. Amazing.