Try ssh'ing onto the box to see what the logs say.

`bosh ssh api_z1 0`

Then,
`cd /var/vcap/sys/log/`

There are plenty of logs to look through, I'd start by running `monit summary` (make sure to be root) to see if any process is failing. If there is a process failing then look at its respective logs. Else start with cloud_controller_ng log directory.