Underlying problem is not solved, but I got around this issue by opening Task Manager and choosing "Bring to Front" for the Activation Manager. This brought it to the front so that I could sign in and get past the frozen, screen-hogging Bug Report dialog.
Baptiste, is there a way to prevent this from happening again? I don't understand why I continue to get a Bug Report dialog every time I open Alchemist even though it did not crash upon closing.