C-SPC works; C-u C-SPC doesn't. How could be?

[Ypo]

Hi

I have a weird problem that only happens in org-mode. I know very little, but I can't think how could this could be possible:

C-SPC works, but

C-u C-SPC doesn't work.

In emacs -q it works as it should, though.

C-h k C-SPC returns:

C-SPC runs the command set-mark-command (found in global-map),
which is an interactive native compiled Lisp function in
‘simple.el’.

It is bound to C-@, C-SPC.

(set-mark-command ARG)

...

C-h k C-u C-SPC returns:

C-u C-SPC is undefined