Error message while trying to edit the Woocommerce checkout page

When I try to edit the Woocommerce checkout page in Cornerstone I get an error message.
Editing the Woocommerce cart page works without issues.
Pro theme and Cornerstone are up-to-date.
I tried increasing the PHP memory limit but with no result, even with the highest setting. I’m using PHP 8.3.
I removed all installed plugins, Custom CSS / JS, changed Child theme for the Pro theme. All with no result.
The error message is:

Screenshot from 2025-11-07 16-38-42

I hope someone can help me out.
Thamks

Hi Rene,

Thanks for reaching out.
There might be some different reasons behind your issue. I want to suggest troubleshooting the following common issue, even if you have already performed some of it, to help us recognize the reason.

1.Theme Related Issue
2.Plugin Conflict
3.Theme Update related issue
4.Child Theme Related issue **if you have activated it.
5.CSS/JS Customization
6.Disabling Cache
7.Disabling CDN
8.Increasing PHP Memory Limit

If you discover that an issue is coming from a custom code or 3rd third-party plugin, kindly consult with a developer or contact the plugin author. Please note that we do not provide support for custom codes and 3rd party plugins, unless you are subscribed to One. If not subscribed, kindly consult with a developer or contact the plugin author.
Please note that we do not provide support for custom codes and 3rd party plugins, unless you are subscribed to One service.
If none of the above helps, please provide login credentials for your site in a secure note to examine it further, 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