Spotted on group0 after the php-1.32.0-wmf.999 branch rolled out to group0 last night.
All occurrences appear to be coming from terbium.
An example in logstash: https://logstash.wikimedia.org/app/kibana#/doc/logstash-*/logstash-2018.06.15/mediawiki/?id=AWQCfpuGoOODFPKvnRn0
Stacktrace:
[{exception_id}] {exception_url} Exception from line 78 of /srv/mediawiki/php-1.32.0-wmf.999/extensions/CirrusSearch/includes/MetaStore/MetaSaneitizeJobStore.php: Wrong document type #0 /srv/mediawiki/php-1.32.0-wmf.999/extensions/CirrusSearch/maintenance/saneitizeJobs.php(395): CirrusSearch\MetaStore\MetaSaneitizeJobStore->update(Elastica\Document) #1 /srv/mediawiki/php-1.32.0-wmf.999/extensions/CirrusSearch/maintenance/saneitizeJobs.php(294): CirrusSearch\Maintenance\SaneitizeJobs->updateJob(Elastica\Document) #2 /srv/mediawiki/php-1.32.0-wmf.999/extensions/CirrusSearch/maintenance/saneitizeJobs.php(84): CirrusSearch\Maintenance\SaneitizeJobs->pushJobs() #3 /srv/mediawiki/php-1.32.0-wmf.999/maintenance/doMaintenance.php(94): CirrusSearch\Maintenance\SaneitizeJobs->execute() #4 /srv/mediawiki/php-1.32.0-wmf.999/extensions/CirrusSearch/maintenance/saneitizeJobs.php(458): include(string) #5 /srv/mediawiki/multiversion/MWScript.php(100): include(string) #6 {main}