Register page not call mail / activation function

Hi Vibe, We have problem with Register page after upgrade to 1.2 modern theme / to 2.4 BuddyPress. Before that when users register, they do receive email to activate account. So far it no long happen, user becomes student immediately and no need to activate account, not receive any mails. We checked email still is sent out to user and web admin when we create new user at backend, when reset password on BuddyPress front end. We are doubt Register page not call mail function. We double check at SendGrid's end and figure out there are no triggers (process, delivery) is raised when we complete Register, whislt the above pages have. We think Register page not call mail / activation function properly. We checked settings of BuddyPress, Page tab shows Register / Activatation point to existing page of WP. Would you please help to us to close this case. Many thanks.