Generating code cache seems buggy in combination with auth code if code cache does not exist.
Steps to reproduce:
Install example client.
Purge code cache (Administration -> System -> Purge, Select all clients and delete the code cache).
Go to Content -> Articles -> Protected Area. Go to properties of Protected Area article.
Select "Article with category" under "Article link" and open the generated URL.
At first access "template.front.loginform.html" is output.
Reload the page: Login form HTML is properly output.