The error Request failed with status code 403 in Joomla (with a message from Axios, so it's probably JS/AJAX in the background) means that the browser received a Forbidden response from the server when it tried to save the page via an HTTP request.
Some extensions (e.g., Admin Tools Pro, Akeeba Web Application Firewall) or modules ModSecurity on the server block POST requests if they contain “suspicious” data.
Browser Error Console on Page view tells that

So yes, I would disable ModSecurity for 15min and recheck. The same with CloudFlare.
If will help, you have to make SPPB trusted in that software. Hosting Support should help more. My options are limited.