Magic Keyboard - numbers not working without holding fn key

Hi,

I have an annoying issue with my Magic Keyboard (no numeric pad).

For some reasons, the numbers are not working when I hit the keys but it is not a hardware problem.

However, the other symbols on the same keys work fine and if I hold the "fn" key the numbers are working fine also.

It happened to me few weeks ago and I have been able to fix it by doing a shortcut including shift+delete but I can't remember the correct combination.

How can I fix it please?

Does anyone even know what this shortcut is supposed to be?