Delay for send e-mail

I use the cronjob system and I have an problem in IC5. For send mail for new members registered or any type e-mail sending !

I even thought the problem was related to the SendGrid integration, but I believe the problem is not there.

I was planning to report this as a BUG, but I need to do more testing.

New members are registering and are not receiving emails quickly, often there is a significant delay.

But if I send a test email to the member's email address, the emails start to be received quickly.

Any suggestions as to what this could be?