I just experienced this issue. My FB data shows that for today, I have 44 view contents, 18 ATC and 1 checkout initiated (it's at 11:40am here now). However, Shopify only shows that my website has only had 10 visits and 10 unique visitors.
What could be the issue? Frequency shows 1.05, Link Clicks 5 and Button Clicks 2.
Why does it show 44 view contents when I have only had 10 visitors?