Hi Peter, thanks for your reply.
I've tried this in LocalWP and live development setup. The setup is a clean installation, without pages with a few plugins activated. Using BricksBuilder as a theme in WP 6.2. Deactivating plugins and switching themes did not solve the issues. It is a simple setup in MetaBox using a CPT and custom field groups (with group fields). The group fields seem to be causing the problem. Creating a new post or modifing post generates the errors. All MB extensions are active. PHP v8.0 and v8.1, Apache server.
The export of the custom field group:
https://pastebin.com/VsqhuwFH
Many thanks for giving it a shot in your local site setup! Please let me know if you need anything else for testing.