Hey there @Liana_Gk
Thanks for reporting this I've tried myself on this course as well on another one and got the same error message on both courses trying to leave a comment from the main site tutorial page. Clicking on Continue the discussion on the forums and leaving a comment directly on the forums is working fine, so right now if you'd like to leave a comment that's the only way to do it.
Reporting this to S.A team so they can have a look
FYI --> @bryan_spence @phil_johnston