I noticed an odd-feeling error while playing with a frontend AJAX call from a localhost server that fetched data from a Google Sheet via a Google Apps Script middleware script.
Any time there was any kind of error in the Google Apps Script code. The JSON-P-based front end call was receiving this message (using the Chrome dev tools Console):
Cross-Origin Read Blocking (CORB) blocked cross-origin response https://script.google.com/macros/s/-yourScriptID-/exec?action=rd with MIME type text/html. See https://www.chromestatus.com/feature/5629709824032768 for more details.</code>
Technically, of course, it was a showing up as a CORS (Cross Domain Resource Sharing) or CORB (Cross Domain Read Blocking) error.