There has been a few changes that have happened recently with Facebook Ads.
If you go within Shopify, you can now customize the level of tracking that occurs between Shopify and Facebook:
The interesting thing here is that by sharing all of the data directly from Shopify with Facebook, Facebook says it can reach even more customers.
Facebook also recently announced a change that ads will be reporting back attributions that happen inside of a 7 day attribution reporting window, from the 28 day window. Now it seems that it reversed course and leaving it at the 28 day window.
Update Dec. 23, 2020: With the latest iOS 14 change impacting Facebook Ads, relying on conversion API will be even more necessary. Now the attribution is on 7 day with 28 day no longer being available.