Still investigating the root cause of why this fails to attach. However, there are also issues detaching the device. This is a clear bug and is being tracked via rbhz#1848417.
Device attach bug is due to a change in packages on the host in OSP 16 and is tracked via rhbz#1848610.
Removing z1 TM, please follow the 16.1.1 inclusion process to have it added.
According to our records, this should be resolved by openstack-nova-20.3.1-0.20200626213433.38ee1f3.el8ost. This build is available now.