To anyone reading this, I’ve fixed it. The details can be found here in my post in another thread here: Testing Intel Optane P1600X, P4800X, P5800/5801X real world performance - #15 by ParanoidAndroid
Essentially, I needed to nuke the drive by using Intel’s MAS CLI tools on Ubuntu and use the sanitize block argument. NVMEformat or Delete arguments would NOT work. While I was there I also set the LBA format to Native 4K, but that wouldn’t have changed anything.