Whenever I try to login to the mobile website of meta, I get the following error:
There seems to be a problem with your login session; this action has been canceled as a precaution against session hijacking. Please resubmit the form.
This is on Firefox Nightly 63.0a1 on a Debian GNU/Linux. On Chromium Version 66.0.3359.117, I get
Central user log in
No active login attempt is in progress for your session.
The above error message are shown when trying to login directly to the meta mobile site without being logged in other wikis. When I am logged-in any other wiki (e.g. enwikipedia), the login page redirects me back without logging me in to where I was and shows the CentralAuth message as shown below.
I could reproduce this on multiple devices.