I know, and maybe it was a coincidence, but when I changed those values, the error started happening.
Adding here some of the errors I'm getting:
[2019-10-30T14:13:19,567][WARN ][logstash.outputs.elasticsearch] Could not index event to Elasticsearch. {:status=>400, :action=>["index", {:_id=>nil, :_index=>"logstash-2019.10.30", :_type=>"doc", :routing=>nil}, #<LogStash::Event:0x51c46abb>], :response=>{"index"=>{"_index"=>"logstash-2019.10.30", "_type"=>"doc", "_id"=>"XnEDHW4BAwjYVExVfrLz", "status"=>400, "error"=>{"type"=>"illegal_argument_exception", "reason"=>"Limit of total fields [3000] in index [logstash-2019.10.30] has been exceeded"}}}}