that was one of the suggestions in this post Pipelines.yml ignored on logstash running as a service
to change line below in /etc/systemd/system/logstash.service
ExecStart=/usr/share/logstash/bin/logstash "--path.settings" "/etc/logstash"
to
ExecStart=/usr/share/logstash/bin/logstash
But I've reverted the change