Everything goes as it should, I can select my repository from dropdown list. But after confirmation (yes, I want to lose all my code) all I get is box shaking and nothing. I tried in browser (firefox 50.0 on linux) and while running from steam.

In firefox I was able to peak under the hood. https://screeps.com/api/user/github-repo returns 200, but in response:

{"error":"TypeError: First argument must be a string, Buffer, ArrayBuffer, Array, or array-like object."}

You have to check what it means... But if there is email somewhere it probably does not handle + (plus sign) well? It happened in different places before...