This is a strange one.
Background: We have a Mediawiki instance for internal (engineering-related) documentation. It's behind a VPN and uses the LDAP Authentication plugin. Mediawiki version 1.28.0, PHP version 5.6.29, MariaDB version 10.1.20-MariaDB-1~jessie. I assume that PHP is using 100% default settings because I did not write a php.ini and indeed cannot even find one.
Problem: Most of the time, when I try to log in, it fails, and I get an error message stating, "Unable to continue login. Your session most likely timed out." Attempting to log in again does not work and simply yields the same error. What's weird is that once in a while it works and I can log in. Further, I am the one who set up and manages this wiki and out of hundreds of users, I appear to be the only one with this problem or I would have definitely heard about it by now.
This happens under Chromium 55.0.2883.87. I have tried disabling all extensions. I have tried removing all cookies and local data for the wiki domain multiple times. It even happens in incognito mode. No issues with Firefox but that is not my daily browser and don't need to have yet another browser window open all the time. I have verified that the both server time and local time are correct.
I highly appreciate any and all suggestions.