Resolving T237551 has immediately revealed another issue with dispatching on beta that seems to have started happening in the last 22-24 hours.
https://wikidata.beta.wmflabs.org/wiki/Special:DispatchStats
Looking at the logs for dispatching (method of which these can be seen below)
ssh deployment-mwmaint01.deployment-prep.eqiad.wmflabs addshore@deployment-mwmaint01:/var/log/wikidata$ tail -f dispatchChanges-wikidatawiki.log
20736: Starting dispatcher Fatal error: Class 'Memcached' not found in /srv/mediawiki/php-master/includes/objectcache/ObjectCache.php on line 186 Fatal error: Uncaught TypeError: Argument 1 passed to MWExceptionHandler::prettyPrintTrace() must be of the type array, string given, called in /srv/mediawiki/php-master/includes/debug/logger/monolog/LineFormatter.php on line 153 and defined in /srv/mediawiki/php-master/includes/exception/MWExceptionHandler.php:364 Stack trace: #0 /srv/mediawiki/php-master/includes/debug/logger/monolog/LineFormatter.php(153): MWExceptionHandler::prettyPrintTrace('#0 [internal fu...', ' ') #1 /srv/mediawiki/php-master/includes/debug/logger/monolog/LineFormatter.php(83): MediaWiki\Logger\Monolog\LineFormatter->normalizeExceptionArray(Array) #2 /srv/mediawiki/php-master/vendor/monolog/monolog/src/Monolog/Handler/AbstractProcessingHandler.php(37): MediaWiki\Logger\Monolog\LineFormatter->format(Array) #3 /srv/mediawiki/php-master/vendor/monolog/monolog/src/Monolog/Logger.php(344): Monolog\Handler\AbstractProcessingHandler->handle(Array) #4 /srv/mediawiki/php-master/vendor/monolog/monolog/src/Monolog/Logger.php(707): Monolog\Logger->addRecord( in /srv/mediawiki/php-master/includes/exception/MWExceptionHandler.php on line 364 20736: Dispatcher exited with 255
Which indicates a problem @ https://github.com/wikimedia/mediawiki/blob/master/includes/objectcache/ObjectCache.php#L186
Which hasn't been tocuhed in 9 years.