Hi
I validated your gtin as well. Your product data looks correct. Everything looks right from your end. Maybe it is the default Shopify app’s problem, as @EmmanuelFlossie pointed out.
You can use any third-party app (I am biased towards our app, obviously 
) and see if this fixes your issue. All the apps usually have a free trial, and you should be able to see whether this issue is fixed within that trial period.
If you use our app, feel free to mention my name, and I will instruct my team to ensure all your GTIN-related issues are looked at.