We've now fixed the issue causing problems with login.
Posted 3 months ago. Jan 15, 2019 - 10:41 CET
We are currently seeing reports from Wunderlist on all platforms about issues with Social Sign In failing (Microsoft / Google / Facebook). Our team is currently working on getting this fixed as quickly as possible.
You can still sign in to your account by going through the regular Sign In option and typing your email address and password.