Hi,
With the current information it is difficult to determine a specific cause, but this can occur if due to lack of resources one of the services fails to start at boot up.
I recommend finding out a specific period of time when this has failed and looking at the logs around that time for specific errors. The relevant files are: /var/log/filebeat/filebeat*, /var/log/elasticsearch/* and var/ossec/logs/wazuh/*/*/*.log*
Please, let us know if you have any more questions.
Best Regards,
Juan C. Tello