comments cannot be seen

Hi,

I have problem where some people who visit my website cannot see all the comments that exist. When they load a page they see some of the comments, next time when they load, they cannot see any comment at all.
I can see all the comments since I’m Administrator user.
I have setup that it is not neccessery for user to login or register to leave or read a comment.
Only few users that are registered can see all the comments.

Please advice!

Thanks.