Macbook 12 fn keys not working

Hi everyone,

I recently got my MacBook 12 2015 back from repair due to short-circuited battery from a previous repair. The functions keys seems to not working properly.

When pressed they do nothing, apart from F11 which does the "dock focus" instead of the "volume down".

If I check the "use fn keys as standard" they emit a sound but still they do nothing (they just emit a sound) or they do something wrong.

Using the keyboard viewer I see that the key press is correctly recognized but the functionality is not activated. If I click the same key on the viewer it works perfectly. It also works fine using an external keyboard.

Already tried doing PRAM and SMC reset.

My only thought at this point is that there is a wrong mapping of some king otherwise I cannot explain myself why they're recognized using the viewer but still they don't do nothing.

Any idea to how to solve this problem?

I try to leave a demonstrative gif of the issue where first I try to press the keys from the keyboard and then I do the same using the cursor.

Thank you all