Weird. I wonder if this is somewhat related to T181869.

The second screenshot is something I have seen while experiencing T179941 (which I do not currently as my non-persistent linux distro is reset several times since reporting that task)

I will quote from T169261#3452695:

Authentication bugs are notorious for having similar symptoms with different causes, since the symptom is usually "I can't log in" or "I get logged out unexpectedly" and there are many things that can cause that, including actual MediaWiki bugs, browser bugs, mysteriously-corrupted cookies that never get enough information to be investigated, and user error such as blocking first- and/or third-party cookies from our sites. And then people tend to assume their problem is the same as someone else's.

Which is why we usually ask people with authentication problems to try several things:

• Report exactly what happens, since "login submits successfully but I'm not logged in", "I'm logged in for the first page-view but logged out when I click any link", "'a loss of session data' when trying to log in", and so on all point to different causes. The last can even point to different things depending on when exactly in the process it occurs.
• Clear all cookes and try again, to see if it's screwed-up cookies.
• Log in using a different browser/device, to see if it's something screwed up in the browser.
• Log in to a different account, perhaps even a newly-created account, to see if it's something wrong with the original account.
• Capture the HTTP requests and responses so we can look for subtle signs of how exactly things are failing.

See also https://www.mediawiki.org/wiki/Manual:How_to_debug/Login_problems

In T181876#3805505, @Aklapper wrote:

I will quote from T169261#3452695:

Authentication bugs are notorious for having similar symptoms with different causes, since the symptom is usually "I can't log in" or "I get logged out unexpectedly" and there are many things that can cause that, including actual MediaWiki bugs, browser bugs, mysteriously-corrupted cookies that never get enough information to be investigated, and user error such as blocking first- and/or third-party cookies from our sites. And then people tend to assume their problem is the same as someone else's.

Which is why we usually ask people with authentication problems to try several things:

• Report exactly what happens, since "login submits successfully but I'm not logged in", "I'm logged in for the first page-view but logged out when I click any link", "'a loss of session data' when trying to log in", and so on all point to different causes. The last can even point to different things depending on when exactly in the process it occurs.
• Clear all cookes and try again, to see if it's screwed-up cookies.
• Log in using a different browser/device, to see if it's something screwed up in the browser.
• Log in to a different account, perhaps even a newly-created account, to see if it's something wrong with the original account.
• Capture the HTTP requests and responses so we can look for subtle signs of how exactly things are failing.

Bunch of thanks for the info Aklapper, I have logged in via another browser and it is working now. :)