"JSON.parse: unexpected character at line 1 column 1 of the JSON data" on privacy settings page, as well as when trying to submit the form

[Grug2021]

When I try to submit the form on my website, I get the following error in Firefox.

JSON.parse: unexpected character at line 1 column 1 of the JSON data

In Chrome, the error is

Unexpected token < in JSON at position 0

I also get this on the Privacy Settings page.

The issue persists with other plugins disabled and using default themes.

Short Debug Information
WordPress Version: 5.7PHP Version: 5.6.40MySQL Version: 5.7.31Caldera Forms Version: 1.9.4WP_DEBUG: