Tried to sign up using the iOS app (because http://mapillary.trydiscourse.com/t/log-in-nightmare/2772).
First password rejected because it didn’t contain an uppercase character. Added uppercase character. Password accepted but sign-up fails.
Trying the same via the website indicates it also needs a non-alphanumeric. Add a non-alphanumeric to the sign-up on the iOS app, and it goes through fine.
Bug: The password requires a non-alphanumeric, but the iOS app accepts a sign-up password without one, then fails without explanation.
iOS app, version 4.9