We have been working with one of the auto deploy Configuration, and an auto deployed ESXi host failed To Boot Up with “Error Loading /vmw/rbd/host//waiter.tgz Fatal Error: 15 (Not Found)” error. While I was troubleshooting the issue, we noticed that, it was something related to certificate expiration as per the VMware KB article 2148040.
Actual error message was this and it stopped working after the restart of the ESXi host, and allowing it to pull up the auto deploy configuration.
Host Failed To Boot Up: Error Loading /vmw/rbd/host//waiter.tgz Fatal Error: 15 (Not Found)

It was not due to the certificate expiration of the hosts, and it was an issue with the time synchronization of the vCenter server. I was able to easily fix it without going in to some deeper level of certificate recreation or renewal.
I hope this post will give you a heads up before you start a time consuming troubleshooting session with your VMware ESXi host, and the auto deploy server.
Read More: Think Twice Before You Restart A VMware VCHA Enabled vCenter Server