Hey @firstname.lastname@example.org! Sorry for the trouble! Did you add that email to the sequence after those subscribers had already received the one before it? If so, there may be a processing delay before it sends out (most likely it'll send the following day at the sequence send time).
That said, I can see you posted this question yesterday —so if it still hasn't sent by now, I'd recommend reaching out to our team via email@example.com (or the in-app messenger in your account) with the name of the Sequence and a description of the issue. One of our Product Specialists will take a look as to whether there might be a setting or something preventing it from going out :)