After I disabled comments globally, all my articles have this error:

Notice: Undefined property: stdClass::$numOfComments in C:\xampp\htdocs\sinteg\components\com_k2\views\item\view.html.php on line 264

Any tips on how to get rid of it? (Besides, re-enabeling commenting..)

Thanks

This is a notice, not an actual error.
It will not affect your site's functionality in any way.

In a production site you should disable error reporting ( Global Configuration menu, server tab. )

Great, nothing to worry about then! Thanks so much for your quick reply.

You 're welcome JJ.