Confirmation Email Can't be Modified or Removed

[TLBS-SIC]

We are building a new storefront on top of an old one. There is an email confirmation that is going out when a sale is made, and I've been unable to find where and how to modify this email. I'm aware of the notifications section, and the customer notifications subsection with the order confirmation field, but this does not appear to be where this confirmation is coming from (the field is empty, and sending a test email sends the default setup, not the custom setup that is sent when an actual order is placed). I'm assuming it's some sort of custom email setup using a custom email template. 

I would be happy to just remove this notification, and use the existing tools moving forward, but can not figure out how to disable it. Ideally I'd disable without deleting it, but I'd settle for just removing it entirely.

[JayAdra]

Do you have any third-party apps which might be sending the email?

Also worth considering that the order confirmation email (and others like it) have a lot of conditional liquid code, so the content might change between preview and actual order.

[TLBS-SIC]

We do have third-party apps that could be involved, especially mail-chimp, which we use to send newsletters and such. I haven't been able to find any sign of a confirmation email though. Only the newsletter functions.

The other apps we use seem doubtful to me to be a factor, but here's a full list: Appstle, Catch Weigth Order Fulfillment, Zapiet, Matrixify, Thinkific, and Collections Import Export Pro. 

[JayAdra]

Maybe check in Shopify Flow if there's anything set up in there?

Otherwise not sure sorry.