We are using cookie share with following settings:
$wgSharedDB = 'wikidata';
$wgCookieDomain = '.moegirl.org';
$wgCookiePrefix = "moegirlSSO";
There used to be some users complain that session lost if they stay in editing interface for hours, but they CAN successfully submit editing, when they saw "lost session data" and click save again.
However, after upgrade to MW1.28, no one can submit editing anymore. We realized that the session ID will change every time user visit a new page/ refresh page/ and submitting edits.
There were no problem for single test wiki in our test, but it break immediately in production environment.
this bug can be reproduced if you login here https://zh.moegirl.org/index.php?title=Special:%E7%94%A8%E6%88%B7%E7%99%BB%E5%BD%95&uselang=en
Press F12 and then you can see the session id change every time you refresh webpage.