Weird behaviour with JS split in a long string

What I’m trying to do with this code is to get all text after the “phraseToFind” from this really long string, but it just logs something completely different. In fact regardless of whatever I put in phraseToFind it just gives something unexpected.

Sorry character limit was exceeded had to put it in a pastebin. Sorry for the inconvenience.

Code with the long string:
https://pastebin.com/gzqh08MS

Rest of the code :

const phraseToFind = "metadataText ":null,"text ":{"textDirection ":"FIRST_STRONG ","text ":"";


const startIndex = x.indexOf(phraseToFind);


if (startIndex !== -1) {
  const result = x.slice(startIndex + phraseToFind.length);
  console.log(result); 
}