Looks like what's happening here is that trying to get a centralauth token can potentially cause saveSettings() to be called. This worries me a bit because it's a write operation and getAuthToken() sounds like it shouldn't write.
2016-07-18 08:15:45 [V4yQLgpAIDEAAFiapTwAAABO] mw1306 mediawikiwiki 1.28.0-wmf.10 exception ERROR: [V4yQLgpAIDEAAFiapTwAAABO] [no req] MWException from line 2609 of /srv/mediawiki/php-1.28.0-wmf.10/extensions/CentralAuth/includes/CentralAuthUser.php: CAS update failed on gu_cas_token for user ID '47226922' (read from master); the version of the user to be saved is older than the current version. {"exception_id":"V4yQLgpAIDEAAFiapTwAAABO"}
[Exception MWException] (/srv/mediawiki/php-1.28.0-wmf.10/extensions/CentralAuth/includes/CentralAuthUser.php:2609) CAS update failed on gu_cas_token for user ID '47226922' (read from master); the version of the user to be saved is older than the current version.
#0 /srv/mediawiki/php-1.28.0-wmf.10/extensions/CentralAuth/includes/CentralAuthUser.php(2558): CentralAuthUser->saveSettings()
#1 /srv/mediawiki/php-1.28.0-wmf.10/extensions/CentralAuth/includes/CentralAuthUser.php(601): CentralAuthUser->resetAuthToken()
#2 /srv/mediawiki/php-1.28.0-wmf.10/extensions/CentralAuth/includes/api/ApiCentralAuthToken.php(62): CentralAuthUser->getAuthToken()
#3 /srv/mediawiki/php-1.28.0-wmf.10/includes/api/ApiMain.php(1435): ApiCentralAuthToken->execute()
#4 /srv/mediawiki/php-1.28.0-wmf.10/includes/api/ApiMain.php(477): ApiMain->executeAction()
#5 /srv/mediawiki/php-1.28.0-wmf.10/extensions/Echo/includes/ForeignWikiRequest.php(62): ApiMain->execute()
#6 /srv/mediawiki/php-1.28.0-wmf.10/extensions/Echo/includes/ForeignWikiRequest.php(117): EchoForeignWikiRequest->getCentralAuthToken(User)
#7 /srv/mediawiki/php-1.28.0-wmf.10/extensions/Echo/includes/ForeignWikiRequest.php(97): EchoForeignWikiRequest->getQueryParams(string)
#8 /srv/mediawiki/php-1.28.0-wmf.10/extensions/Echo/includes/ForeignWikiRequest.php(30): EchoForeignWikiRequest->getRequestParams()
#9 /srv/mediawiki/php-1.28.0-wmf.10/extensions/Echo/includes/NotifUser.php(710): EchoForeignWikiRequest->execute()
#10 /srv/mediawiki/php-1.28.0-wmf.10/extensions/Echo/includes/NotifUser.php(741): MWEchoNotifUser->getForeignData()
#11 /srv/mediawiki/php-1.28.0-wmf.10/extensions/Echo/includes/NotifUser.php(489): MWEchoNotifUser->getForeignCount(string)
#12 /srv/mediawiki/php-1.28.0-wmf.10/extensions/Echo/Hooks.php(1147): MWEchoNotifUser->resetNotificationCount()
#13 /srv/mediawiki/php-1.28.0-wmf.10/includes/Hooks.php(195): EchoHooks::onUserSaveSettings(User)
#14 /srv/mediawiki/php-1.28.0-wmf.10/includes/user/User.php(3955): Hooks::run(string, array)
#15 /srv/mediawiki/php-1.28.0-wmf.10/includes/auth/AuthManager.php(1693): User->saveSettings()
#16 /srv/mediawiki/php-1.28.0-wmf.10/extensions/CentralAuth/includes/CentralAuthUtils.php(141): MediaWiki\Auth\AuthManager->autoCreateUser(User, string, boolean)
#17 /srv/mediawiki/php-1.28.0-wmf.10/extensions/CentralAuth/includes/CreateLocalAccountJob.php(56): CentralAuthUtils::autoCreateUser(User)
#18 /srv/mediawiki/php-1.28.0-wmf.10/includes/jobqueue/JobRunner.php(265): CentralAuthCreateLocalAccountJob->run()
#19 /srv/mediawiki/php-1.28.0-wmf.10/includes/jobqueue/JobRunner.php(179): JobRunner->executeJob(CentralAuthCreateLocalAccountJob, BufferingStatsdDataFactory, integer)
#20 /srv/mediawiki/rpc/RunJobs.php(47): JobRunner->run(array)
#21 {main}