Mail app replying to myself not the other person

So if I’m in an email chain, and I respond to the email it responds properly. However, if I need to send another email replying (before they return mine), the reply always gets sent to me and not the other person. Why is this happening?

Person A mails Me. I respond to Person A. (This is sent properly). I send a second reply to Person A (this is now sent to me and not Person A).