This is an accepted solution.
Nick here from Shopify.
This often occurs when the DNS settings aren't correct on your domain. Can I ask where you bought your domain from and if you can check the DNS settings for me, please? You can check this from the DNS checker website here also.
Shopify also has a guide for setting up third party domains with the correct DNS settings here.
Could you also share a link to your store so I can take a closer look? Is it also just happening on one of your domains or all of them? Let me know.
All the best, Nick