What could cause this error following enterprise-search restart?

I followed these steps for the installation.

Copying and pasting these lines into Elasticsearch, kibana and enterprise-search yaml files

Changed the permissions of var/log/enterprise-search folder and contents (see screenshot below)

And everything started fine.

Then, I switched-off and then on and got this error message:

Any suggestions?

d@vmm:~$ sudo systemctl start Elasticsearch.service
Job for Elasticsearch.service failed because the control process exited with error code.
See "systemctl status Elasticsearch.service" and "journalctl -xeu Elasticsearch.service" for details.

Can you please check the underlying Elasticsearch logs, usually /var/log/elasticsearch.