Finally managed to register, after choosing a user name verbose enough that it didn't cause "too similar to existing username" errors anymore. Phew.
Committed identity: 25a7f2160ec377e897950c8b0da97a36d9fa414c3c5e04338a8ece8a058bbc83e1d4033e50634bc4c12316cf235bcaeca89b745a3e668ebaa215a7a29bc7ae38 is a
SHA-512 commitment to this user's real-life identity.