Also, from the log, I see your ES version is 5.6:

at org.elasticsearch.bootstrap.Elasticsearch.init(Elasticsearch.java:136) ~[elasticsearch-5.6.16.jar:5.6.16]

and I'm not sure why - in v0.16, the ES version is already 7.6, which makes me think your original version was v0.15, also in the new docker-compose the version is 7.16, so maybe you are not using the updated docker-compose file?

It confused me too, but ES dir in my 0.16 version is /opt/trains/data/elastic_7