```name=Error message
Serialization of 'Closure' is not allowed
```
```lines=12,name=Stack Trace
from /srv/mediawiki/php-1.36.0-wmf.28/includes/libs/objectcache/MemcachedPeclBagOStuff.php(228)
#0 /srv/mediawiki/php-1.36.0-wmf.28/includes/libs/objectcache/MemcachedPeclBagOStuff.php(228): Memcached->cas(integer, string, array, integer)
#1 /srv/mediawiki/php-1.36.0-wmf.28/includes/libs/objectcache/MediumSpecificBagOStuff.php(355): MemcachedPeclBagOStuff->doCas(integer, string, array, integer, integer)
#2 /srv/mediawiki/php-1.36.0-wmf.28/includes/libs/objectcache/MediumSpecificBagOStuff.php(316): MediumSpecificBagOStuff->cas(integer, string, array, integer, integer)
#3 /srv/mediawiki/php-1.36.0-wmf.28/includes/libs/objectcache/MediumSpecificBagOStuff.php(268): MediumSpecificBagOStuff->mergeViaCas(string, Closure, integer, integer, integer)
#4 /srv/mediawiki/php-1.36.0-wmf.28/includes/libs/objectcache/wancache/WANObjectCache.php(781): MediumSpecificBagOStuff->merge(string, Closure, integer, integer)
#5 /srv/mediawiki/php-1.36.0-wmf.28/includes/libs/objectcache/wancache/WANObjectCache.php(1600): WANObjectCache->set(string, array, integer, array)
#6 /srv/mediawiki/php-1.36.0-wmf.28/includes/libs/objectcache/wancache/WANObjectCache.php(2570): WANObjectCache->fetchOrRegenerate(string, integer, Closure, array, array)
#7 /srv/mediawiki/php-1.36.0-wmf.28/includes/deferred/MWCallableUpdate.php(38): WANObjectCache->{closure}()
#8 /srv/mediawiki/php-1.36.0-wmf.28/includes/deferred/DeferredUpdates.php(513): MWCallableUpdate->doUpdate()
#9 /srv/mediawiki/php-1.36.0-wmf.28/includes/deferred/DeferredUpdates.php(390): DeferredUpdates::attemptUpdate(MWCallableUpdate, Wikimedia\Rdbms\LBFactoryMulti)
#10 /srv/mediawiki/php-1.36.0-wmf.28/includes/deferred/DeferredUpdates.php(221): DeferredUpdates::run(MWCallableUpdate, Wikimedia\Rdbms\LBFactoryMulti, Monolog\Logger, BufferingStatsdDataFactory, string)
#11 /srv/mediawiki/php-1.36.0-wmf.28/includes/deferred/DeferredUpdatesScope.php(267): DeferredUpdates::{closure}(MWCallableUpdate, integer)
#12 /srv/mediawiki/php-1.36.0-wmf.28/includes/deferred/DeferredUpdatesScope.php(196): DeferredUpdatesScope->processStageQueue(integer, integer, Closure)
#13 /srv/mediawiki/php-1.36.0-wmf.28/includes/deferred/DeferredUpdates.php(242): DeferredUpdatesScope->processUpdates(integer, Closure)
#14 /srv/mediawiki/php-1.36.0-wmf.28/includes/MediaWiki.php(1117): DeferredUpdates::doUpdates(string)
#15 /srv/mediawiki/php-1.36.0-wmf.28/includes/MediaWiki.php(853): MediaWiki->restInPeace()
#16 /srv/mediawiki/php-1.36.0-wmf.28/includes/MediaWiki.php(865): MediaWiki->{closure}()
#17 /srv/mediawiki/php-1.36.0-wmf.28/includes/MediaWiki.php(587): MediaWiki->doPostOutputShutdown()
#18 /srv/mediawiki/php-1.36.0-wmf.28/index.php(53): MediaWiki->run()
#19 /srv/mediawiki/php-1.36.0-wmf.28/index.php(46): wfIndexMain()
#20 /srv/mediawiki/w/index.php(3): require(string)
#21 {main}
```
##### Impact
Unclear.
Roughly 45 of these seen since deploy of 1.35.0-wmf.28 (T271342) to all wikis.
##### Notes