weird Behaviour

We’ve noticed a weird thing in GA for amp pages.
When a user lands on an AMP page of our site using Google Organic Search, the url on the browser is the typical amp url starting with https://www.google.com/amp/….. and the source in GA is “google” BUT when they click on any other links available on the page, surprisingly the source becomes “direct”!
Why this is happening? Giving us a unrealisticly high direct traffic. Can you guys please help us in fixing this? We’re a bit inexperienced here.
Note: Our GA implementation through GTM
Thanks.