Hi @Kelly - welcome to the community. And I’m sorry you’re running into these issues, even though the background info helps provide some context, it’s a bit tricky to help you resolves these without access to your account. Can you tell us what your “Engagement Group” Segment (I assume) rule or definition is?  You can screen capture it or write it out if it’s simple.  I suspect you are using “Profile Creation Date” which might include people you may have deleted in Klaviyo (but are still in Shopify) that is pulled in when you resynced the data. 

Also, you may want to re-evaluate your Shopify “Accepts Marketing” is False flag for Profiles in Klaviyo.  In some cases, for example when someone starts Checkout (or places an order), they can opt-out of Marketing within Shopify at that time. When they do this, they will have a Shopify Accepts Marketing = False in their Profile.  Though, they may then “Subscribe” to Klaviyo outside of Shopify (example via Klaviyo Signup Forms or third party APIs) - so you need to determine if you want to exclude those in your Engagement Tiers.  If you want to be safe, you can also exclude them, and then fine-tune your rules to include those that Subscribed (but for some reason opted-out in Shopify, it’s a complicated timing issue of which action you take into consideration).  

Here’s a quick reference from Klaviyo about “Accepts Marketing”:

• About the Accepts Marketing Property and Subscribers

If you share your Engagement Tiers Segment Rules, maybe we can help better troubleshoot!

It also sounds like you may need to do some list cleaning if emails are getting sent to contacts that weren’t sent to since ‘97 (if they were suppressed, they should receive further emails unless they subscribe again).

Kindly read these article : https://help.klaviyo.com/hc/en-us/articles/115005078347-Guide-to-List-Cleaning#:~:text=The%20process%20for%20cleaning%20your,or%20deleting%20these%20unengaged%20profiles

You will learn more about how to clean your lists and maintain strong deliverability by identifying and suppressing unengaged profiles.

Let me know, if you’ve any more questions?