Can you share the child theme please?
Well, that is disabling comments from all pages.
We would like to see, any better solution when you update the theme next time.
Thanks for all your help.
Surprisingly, when I change to other theme, this problem does not occur. My guess is the combination of bp and mesocolumn.
I can add the custom css for registration, but it is everywhere like groups/members/activity/forum pages etc, every bp pages. We have to add this piece of code for every bp pages until we have permanent fix.