Does debugging not work offline?

I had no Internet connection this morning and while Construct itself worked fine, debugging was not possible.

I got "The FetchEvent for "https://preview.construct.net/local.html?debug=" resulted in a network error response: the promise was rejected." As an Error in the Console.

I use Construct as an App in Edge and I use it exclusively only for Construct without any plugins.

Question is: Did I do something wrong or is it Edge or does it not work at all offline.