WordPress JSON Error Fix

I'm experiencing a 'Not a valid JSON response' error on my client's WordPress site (https://cariboumaine.org) This error is most often triggered when attempting to update posts or pages. It seems to have arisen without any specific action on my part.

Ideal Skills and Experience:
- Proficient in WordPress debugging and troubleshooting
- Experienced in resolving JSON related issues
- Capable of post/page update error diagnostics
- Familiar with potential implications of WordPress updates and plugin installations

I handle some freelance marketing efforts for a municipality and their Wordpress site was built years ago by someone else. I added a few Elementor pages when I started working with them and over the years, we have had JSON errors randomly pop up off and on every few months or so when trying to update pages and posts. Typically it is when we are adding images. I am not an IT specialist, so I have no idea how to permanently fix the issue. Occasionally, I've been able to work around it, and sometimes it seems to resolve on its own. GoDaddy has been no help at a permanent solution, but they have resolved it for us once or twice. Despite my lack of knowledge and experience, I have unsuccessfully gone through steps I've found online (yet have no real understanding of and hope I've not messed things up even further) multiple times - including but not limited to:

Check WordPress URLs in Settings
Fix WordPress Permalink Structure
Regenerate WordPress .htaccess File
Deactivate All WordPress Plugins
Temporarily Switch to the Classic Editor
Switch to a Default WordPress Theme
Temporarily Turn Off Website Application Firewall
Turn On Debugging in WordPress
Check for Mixed Content Error