Hank here from Shopify.
Would it be possible to share your domain so that I can check what might be the issue? The most common is multiple A records, which can cause the SSL certificate to be delayed.
I will share this guide about connecting your domain, but will also share the below screenshot of what is needed.
Let me know how you get on, or if you share your domain, I will run a few checks on my end.
All the best,