If you provide a relative path to the config file for zabbix_agentd, it fails on startup with errors that are very unhelpful:

Can not create IPC key for path './zabbix_agentd.conf', try to create for path '.' [No such file or directory]

zabbix_agentd -c ./zabbix_agentd.conf was what was attempted to be run.

It seems you need to provide an absolute path. Relative paths should also work.