Cannot open access to console, the root account is locked. RHEL 9 image

I build an EC2 instance based on RHEL 9 using an M7i.4Xlarge image, but due to application licensing had to limit the available cores to 2cpu.

I then wanted to increate the cores, so I used the following procedure:

1. create an AMI image of the original machine
2. terminate original instance (in order to re-use the network interface to preserve the IP address)
3. launch new instance from AMI image in step 1, but specify 4 cores instead of 2
4. Boot new instance

I tested this procedure on a 'test' machine and it worked with no issues. However when I do this with my actual application server, the new instance will not boot. I get the error "Cannot open access to console, the root account is locked."

I've detached the boot/root disk and can attach it to a different instance and read the filesystem. /etc/fstab from the non-booting instance is configured to mount the disks by UUID and not device name (found that suggestion https://repost.aws/questions/QUbkr4v8pBQ8Sz-4AdDVDJQA/cannot-open-access-to-console-the-root-account-is-locked-al2-t2-t3. I also commented out any remote mountpoints in case that was causing problems. So the only mounts in /etc/fstab will be "/", "/boot" and "boot/efi"

Not sure how to proceed at this point, this thing won't boot AT ALL.