If there an js error occurred the replit console tab display only something like

"@https://replit.org/data/web_project/c82c4a76033b78c8b5eb8af1c38a7503/index.js:9:9"

If tampermonkey plugin is running it displays three additional errors like above without any explanation to the error, like above. I have already created a post about that some time ago here: https://repl.it/feedback/p/html-css-js-session-hijacks-console-and-fails-at-it-on-chrome-with-tampermonkey it is similar with firefox