all online demos fail with a heroku error?!

was trying it a few days ago, and for me line demos fail with a "heroku" application error, for example: 
 
https://demos.yjs.dev/codemirror/codemirror.html
https://demos.yjs.dev/atlaskit/atlaskit.html
https://demos.yjs.dev/quill/quill.html

and probably all others fail as well.  