Lulu here from the Shopify Support team. Thanks for reaching out here, and I'll be more than happy to help you out.
This does sound strange and it would definitely be frustrating for you and the customer. When you do a test purchase on your store, does the same happen to you? Can you send me some screenshots if you notice it happening when you test it? It does sound to me like it is theme related. What theme are you using at the moment? When did you notice this issue started to happen? Did you add any new apps or code into your theme? Once I have a bit more information on this issue I can try and help you out or point you in the right direction.
Looking forward to hearing back from you soon.
Lulu | Social Care @ Shopify
- Was my reply helpful? Click Like to let me know!
- Was your question answered? Click Accept as Solution
Could you please provide your website URL so that I can check the issue?