Hi Chris,
I have checked your product URL after logging in and it shows the Add to Cart form. It seems that the issue is related to the Server Level Cache, I would suggest you contact your hosting provider to purge all the server-level cache and check if that resolves your issue.
I would also suggest you update the Pro to its latest version i.e. 5.1.4 and check if that resolves your issue.
If none of the above helps, there might be some different reasons behind your issue. I would like to suggest troubleshooting the following common issue to help us to recognize the reason.
1.Theme Related Issue
2.Plugin Conflict
3.Theme Update related issue
4.Child Theme Related issue
5.CSS/JS Customization
6.Disabling Cache
If that does not solves your issue, please copy your live site to a staging server so we could troubleshoot freely without breaking your live site.
And give us access in the secure note including:
– WordPress Site URL & Login URL
– WordPress Admin username/password
To create a secure note, click the key icon underneath any of your posts.
Thanks