These two schemas have a pretty high volume of errors, at times many errors per second.
You can see errors on event database on eventerror table, Here is an example. There are two wrong field names: type_of_search and app_install_ID neither of which match schema column names: https://meta.wikimedia.org/wiki/Schema:MobileWikiAppiOSSearch
{"event": {"code": "validation", "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%3A6%2C%22ts%22%3A%222018-10-17T21%3A19%3A07%2B01%3A00%22%2C%22primary_language%22%3A%22en%22%2C%22session_id%22%3A%2289DB9A73-2D4B-40BA-A346-9DD4AE79DB3F%22%2C%22session_token%22%3A%22825529FA-7BCF-4AD8-ADE8-9B14A9FFED65%22%2C%22app_install_ID%22%3A%22FF8AA8ED-0CEE-43CE-AB32-6FED18B7B437%22%2C%22time_to_display_results%22%3A404%2C%22type_of_search%22%3A%22prefix%22%2C%22is_anon%22%3Atrue%7D%2C%22schema%22%3A%22MobileWikiAppiOSSearch%22%2C%22wiki%22%3A%22enwiki%22%7D\tcp3042.esams.wmnet\t275283408\t2018-10-18T20:59:59\t82.132.223.121\t\"WikipediaApp/6.0.2.1493 (iOS 11.4.1; Phone)\"", "revision": 18289062, "schema": "MobileWikiAppiOSSearch"}, "recvFrom": "eventlog1002.eqiad.wmnet", "revision": 14035058, "schema": "EventError", "timestamp": 1539896400, "uuid": "c6d49544d31811e8b7e61418775b0d42", "wiki": ""}
Please have in mind that these types of validation errors can be tested on beta before launching to prod:
https://wikitech.wikimedia.org/wiki/Analytics/Systems/EventLogging/TestingOnBetaCluster#How_to_log_a_client-side_event_to_Beta_Cluster_directly