It would seem that I am unable to read a depth buffer as an input attachment.
The depth buffer was written in a previous subpass. Instead of getting values from the depth buffer it would seem that I am just seeing noise.
I have no problems reading a colour buffer as an input attachment.
You can see the noise revealed in this image which was using an in-shader depth test as part of a depth peel.
Thanks very much for reporting this issue to us. We have reproduced the issues you are seeing and we have confirmed that this is caused by a bug in our Vulkan drivers. Due to the nature of this issue we consider it to be of high priority. We cannot confirm when a new driver with this fix will be released although we hope it will happen shortly.