Apex JSON Parsing Error

I am using Database 19c and Apex 19.2

I am busy writing code to parse JSON data received in a CLOB via REST request. I successfully parsed all the JSON received except one piece of JSON that gives the error below, and I cannot figure out why as the content is basically the same as the other JSON I am processing. The code raising errors is seeded and obfuscated so I cannot debug.

I have checked the piece of JSON with multiple online validators and all show it is valid. I have also recoded the embedded base64 encoded document and it is also a valid pdf.