Lots of errors like:
"message": "Additional properties are not allowed (u'app_install_ID', u'ts', u'type_of_search' were unexpected)", "rawEvent": "?%7B%22revision%22%3A18289062%2C%22event%22%3A%7B%22action%22%3A%22results%22%2C%22number_of_results%22%3A29%2C%22ts%22%3A%222018-10-23T22%3A57%3A20-05%3A00%22%2C%22primary_language%22%3A%22en%22%2C%22session_id%22%3A%225A0D538F-D6EA-428A-B5AE-2B625B79ED80%22%2C%22session_token%22%3A%220E45E4EE-A65C-471A-9B49-50A14DE7D700%22%2C%22app_install_ID%22%3A%22B8F2EEE4-AE25-4E1D-B295-898DC2C6221D%22%2C%22time_to_display_results%22%3A518%2C%22type_of_search%22%3A%22full%22%2C%22is_anon%22%3Atrue%7D%2C%22schema%22%3A%22MobileWikiAppiOSSearch%22%2C%22wiki%22%3A%22enwiki%22%7D\tcp1089.eqiad.wmnet\t26710954\t2018-11-01T13:40:43\t66.128.250.69\t\"WikipediaApp/6.0.2.1493 (iOS 12.0.1; Tablet)\"", "revision": 18289062, "schema": "MobileWikiAppiOSSearch"
You can see these in the eventlogging_EventError topic in Kafka, or in the event.eventerror table in Hive.
This morning these ramped up to around 30 / second:
https://grafana.wikimedia.org/dashboard/db/eventlogging?panelId=13&fullscreen&orgId=1&from=1541077076036&to=1541079237576