Another bit on why not to trust Shopify's built in tracking.
I recently found a few 404s happening on a client's Facebook product catalog/carousel ads. Within the same ad, some products would be fine and others would 404. That isn't interesting and it is easily fixable, once you know about it.
What is interesting is that Shopify DOES send a proper 404 status on loading the page, good for them, however, their tracking, Trekkie, doesn't care at all. While we can get that 404 status via the template.name and set that manually to the page type or whatever is useful, Shopify doesn't' do that by default. Meaning you could do a major revamp on your site/products etc, have 404s all over, and it would look like you were still getting results on those products, at least landings etc!
I am just again shocked at how badly Shopify does things like this. The whole concept regarding apps and working with "mashups" of services is amazing, but Trekkie, I wish would go away. Anyway we found a solution for our clients and it isn't that hard, it is just another little hole to fill, and maybe not so little if it hits you. In this case the client moved from Magento and people missed quite a few of these 404s. There is a decent way to find these in Shopify Analytics. Under the Sessions by Social Source.
But EQ does this better. We intercept the 404 page type and fix the PageNames so this issue is totally obvious, including which Campaign/Adset/Ad the error came from.