With my main account, I opted in, out, in, out at beta cluster (over about 10 minutes, with pauses between each).
The final opt-out, resulted in this error:
```
[7375dc8e] /wiki/Special:Preferences MWException from line 3711 of /srv/mediawiki/php-master/includes/User.php: CAS update failed on user_touched for user ID '1255' (read from slave); the version of the user to be saved is older than the current version.
Backtrace:
#0 /srv/mediawiki/php-master/includes/Preferences.php(1439): User->saveSettings()
#1 /srv/mediawiki/php-master/includes/Preferences.php(1450): Preferences::tryFormSubmit(array, PreferencesForm)
#2 /srv/mediawiki/php-master/includes/htmlform/HTMLForm.php(591): Preferences::tryUISubmit(array, PreferencesForm)
#3 /srv/mediawiki/php-master/includes/htmlform/HTMLForm.php(503): HTMLForm->trySubmit()
#4 /srv/mediawiki/php-master/includes/htmlform/HTMLForm.php(518): HTMLForm->tryAuthorizedSubmit()
#5 /srv/mediawiki/php-master/includes/specials/SpecialPreferences.php(70): HTMLForm->show()
#6 /srv/mediawiki/php-master/includes/specialpage/SpecialPage.php(384): SpecialPreferences->execute(NULL)
#7 /srv/mediawiki/php-master/includes/specialpage/SpecialPageFactory.php(553): SpecialPage->run(NULL)
#8 /srv/mediawiki/php-master/includes/MediaWiki.php(249): SpecialPageFactory::executePath(Title, RequestContext)
#9 /srv/mediawiki/php-master/includes/MediaWiki.php(682): MediaWiki->performRequest()
#10 /srv/mediawiki/php-master/includes/MediaWiki.php(476): MediaWiki->main()
#11 /srv/mediawiki/php-master/index.php(41): MediaWiki->run()
#12 /srv/mediawiki/w/index.php(3): include(string)
#13 {main}
```
{F2643708}
----
See also, the possibly related: {T95839}