Seen on en.wikipedia.

Alse see on it.wiki and wikidata. I use Chrome.

Had the same problem on Commons.
Manually removed all "forceHTTPS" cookies from Firefox but it didn't work.
Then deleted all cookies related to "commons.wikimedia.org" and after that could login again.

Probable causes:

• recently disabled "Always use a secure connection when logged in" in my preferences on some wikis (but not on commons)
• recently switched from Chrome to Firefox and imported all history (including cookies) from Chrome into FF using import wizard.

Has anybody still seen this problem recently?
I wonder if it's related to bug 61048.

The initial report sounds like a duplicate of another bug that Kaldari reported a while back (I can't find it at the moment). It was traced to a Varnish issue (Varnish was returning the cached, anonymous version of the page on http requests, after the user had logged in via https).

Bug 61048 only affects non-CentralAuth accounts, but it looks like Dalba is a global account-- https://meta.wikimedia.org/wiki/Special:CentralAuth/Dalba. Dalba, please correct if you were using another account.

I haven't had this problem in a while (probably since my last comment), but at the time I've been editing as user:دالبا (https://meta.wikimedia.org/wiki/Special:CentralAuth/دالبا)

Change 965729 had a related patch set uploaded (by Bartosz Dziewoński; author: Bartosz Dziewoński):

[mediawiki/extensions/CentralAuth@master] Remove success notification when we can't get autologin response

https://gerrit.wikimedia.org/r/965729

Change 965729 merged by jenkins-bot:

[mediawiki/extensions/CentralAuth@master] Remove success notification when we can't get autologin response

https://gerrit.wikimedia.org/r/965729