Unable to show cookies warning

Try to temporarily change to theme Twenty Seventeen. If it works then, then I’m quite sure that you in your own theme have missed one or several of the standard hooks that should be called during different parts of the web-page generation.

Thx for the reply.

I already know that it’s most likely something wrong in my coding.
I just need to know what I must pay close attention to, what the cookies plugins look for to place the cookie bar.

Just dig into the code of the cookie plugin and check to which hook it enqueues its magic function.