Why does script tag insertion via API work inconsistently across domains?

Store Design
1

Hello community!
I have problems with Script Tag insertion via API.

The main problem is:
we have two domain properties, for example
domain - example.com
myshopify_domain - example.myshopify.com (this domain created by default on shopify side)

There are two cases, and need to know why it happens:

  1. We try to insert script on “domain” property and script doesn’t insert. → then we insert script on “myshopify_domain” property and it works.
  2. We try to insert script on “myshopify_domain” property and script doesn’t insert. → then we insert script on “domain” property and it works.

It happens to different domains, and this behaviour is not stable.

Any suggestions?