This domain (cdn.ampproject.org) is Google's "AMP Cache" domain.

That means you're getting organic visitors from Google finding your AMP pages in search results.  That's great! Google delivers your AMP pages from the "cdn.ampproject.org" cache domain.  This is one of the reasons that AMP pages load even faster when coming from a search engine like Google - they are cached.

You may see "referral traffic" coming from "cdn.ampproject.org", because when someone finds your AMP page in Google Search, they are on "cdn.ampproject.org", and then when they click onto your site, then "cdn.ampproject.org" becomes the referrer.  This is completely normal.

What may happen as a result of the "cdn.ampproject.org" referral, is that you may have inflated bounce rates because of sessions not being tracked properly between domains.  There is a solution for this. To prevent the cdn.ampproject.org domain from inflating bounce rates, Google recommends you add a referral exclusion for the domain "cdn.ampproject.org".  We have a blog post on exactly how to do this: https://shopsheriff.com/blog/google-analytics-session-stitching-with-amp-and-shopify

If you need more information about this, you can read about it on Google's support blog here: https://support.google.com/analytics/answer/7486764?hl=en.  When reading the blog, please note that AMP for Shopify uses "Option 3: analytics.js".  Please also note that all of the necessary "linker" parameters and <amp-analytics> scripts are taken care of for you, and all you have to do is add the referral exclusion.