Metron REST fails to start with Ambari, works via CLI

[Laurens Vets]

Before I open a JIRA ticket, does anyone know why starting Metron REST 
fails, but manually starting it with "service metron-rest start 
<password>" works?

In /var/log/metron/metron-rest.log, I see the following:
  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v1.4.1.RELEASE)

Jul 11, 2017 9:43:09 PM org.apache.tomcat.jdbc.pool.ConnectionPool init
SEVERE: Unable to create initial connections of pool.
java.sql.SQLException: Access denied for user 'metron'@'metron' (using 
password: YES)
        at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:964)
        at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3973)
        at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3909)
        at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:873)
        at com.mysql.jdbc.MysqlIO.secureAuth411(MysqlIO.java:4420)
        at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1278)
        ...

But the username & password are correct (tested manually via CLI) and 
manually starting the service works as well... Is Ambari somehow 
forgetting to supply the password? How can I test this?

Thanks in advance!