I have 2 exact same website on Cloudflare and on Amazon Web Services. (1 live website, 1 for testing etc.) On the live website in admin panel when i hit the somewhere ‘Save’ button i receive 403 error on the console. But on the test website no issue.
I have to admit that when I clicked the screenshot, it didn’t bring up the image. Thankfully, zooming in on your post makes the thumbnail readable.
If you get a 403, it’s quite possible that request triggered a Firewall action, and that would show up in Firewall Overview → Events log. Be sure to check your server log if nothing shows up here.