I just checked again a minute ago and now it worked but I think the problem is not really new. I am experiencing problems with loading iD since many weeks - it may take up to 15 minutes after pressing the “edit” button on the main page before the editor opens the editing window and then it still can take another minute or two until the OSM data have loaded.
It is really frustrating to waste such a lot of time waiting instead of being able to do mapping work. I have to add that I did never have these problems before, it startet around half a year ago, some days it’s fine but other days its really bad.
And it’s not only me, other users have reported the same problem in the german subforum repeatedly.