I assume you have double checked the correct configuration of your Task-Actions Mail-Notification?!

Can you try to re-create the action that doesn't send out a mail?

Thanks Philipp

How can I check the correct configuration of my Task-Actions Mail-Notification?. The email task haven´t configuration, only the Subject and Email body.

I re-created the action and sent the email, but I don't understand Why did not sent the email on the other task?

I cannot tell you why it didn't work with the first task. Sometimes there simply are technical issues that can be solved by recreation.

Thanks Philipp