P6289 is the elasticsearch mapping of the current logstash index. We are hitting the 1000 fields per index limit. Just raising that limit is not a good idea, we should sanitize what we send to elasticsearch.
A quick look at that mapping indicates that some log producers are throwing mostly random objects at logstash (we can see fields name like Q27938#X which don't seem to make any sense in logstash.
A dirty count show that the types with most fields are mediawiki, followed closely by restbase. In the mediawiki type, there seem to be a large number of fields generated by eventbus, including some slightly complex objects. (The most fields is more a guess than a precise count).
I see a number of fields starting with err_ and ending with a number. This looks like they should at least be consolidated on the same field.
More analysis is required to actually get anywhere...