This part of the error message looks like there is a problem with the date format setting in your target index. Can you post the mapping you have in Elasticsearch for the "hybriswaiting_database" index? You should get it with something like
curl -X GET "<your_es_adress:your_port>/<your_indec_name>/_mapping"
This means your index is expecting a "date" with the default format, which is "strict_date_optional_time||epoch_millis", so you can index date strings like 2015-01-01 or 2015-01-01T12:10:30Z or plain unix time milliseconds like 1420070400001 but not something that is just a year and month. In order to do that you need to specify a different "format" when the index mapping is created. In the case of Logstash this is sometimes done via and index template, but might also be done manually by yourself. Another option would be to convert your YYYY-MM date to YYYY-MM-01 somewhere in your Logstash pipeline.
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