Basically I am opening an existing SP PAGE BUILDER page and making a text change, then clicking save and getting the error in the picture.

https://prnt.sc/NISlU-Cb7Oq8

details added

Please take a full site backup with Akeeba Backup in ZIP format and share here. Follow this tutorial. I will check it on my localhost.

Hi, you asked for access to the administrator area, I provided this.

So please use that to diagnose the issue, it should need me to provide you a backup of the site.

Thanks

Please share a SUPER USER access.

have updated the shared user to be a superuser

I have checked the backup on my localhost. It works fine here. Please check that if you have mod_security disabled. If not, then ask your hosting provider to disable it. Then check your issue.

ok so checked this with the hosting provider and it was enabled, so got it disabled and now I can save the text page

Question, why is this a problem now, managed to build the site and edit it multiple times previously, so why a problem now?

Also the frontend page editor just loads a blank page when viewing an existing page

I have no knowledge on why this is happening. Rocket loader or mod_security might be blocking the resource loading. This is why turning it off makes things work. After you have done the work, then you may turn it on.