Cannot email more than 2 times with contact replying to marketing email

Hello!

Need some help because I have been struggling with this. I automate quotes after a prospecting customer shares their information via my website. An automation is triggered with a specific email template and then the prospect is put into a deal stage.

Problem: The prospect replies to the email but I can only reply once within the deal email.

Question: What settings or limits does AC have that I have not adjusted in order to reply more than once to the prospect inside deal emails?

Context: After the prospect replies a second time, a new email chain is created automatically IE Re:Re in the email subject line. Not sure if this has something to do with unable to email back because it is a different email chain.

Greatly appreciated !