vCenter 6.7 Update 1 - Converge to embedded failed!
Update 27th October 2018: I was meant to provide this update last weekend, but it has been a hectic week. Within a few hours of posting this issue, a few people at VMware reached out to me to understand more about my configuration, asked me to upload the logs and a few of the smart guys and gals at VMware had been able to reproduce the issue. As it turns out, the key in the APPLMGMT_PASSWORD vecs store is used when a file based backup of the VCSA is scheduled.