Board Thread:Support Requests - Getting Technical/@comment-24173435-20180302214831/@comment-9605025-20180304110656

If you have any custom JS, either personal or site-wide, it may be affecting the editor. Have you made any changes to either your personal or site JS shortly before and/or after this started happening? Are you using any ad blockers? If not (and this is still happening), it is likely just a bug and you should report it using Special:Contact/bug.