Saving custom JS error

When I save any custom JS, It says successful save but when I go back it has disappeared. I also get this error in the console;

fluent-forms-editor.js?ver=6.1.16:2 [Violation] Added non-passive event listener to a scroll-blocking 'touchmove' event. Consider marking event handler as 'passive' to make the page more responsive. See https://www.chromestatus.com/feature/5745543795965952