Netbooting debian with NFS root but cannot get root access

I’m booting debian 12 via PXE and mounting / over NFS. This is seemingly working quite well. I created the disk by installing Debian from the CD onto a disk and mounting it onto /mnt/debian on my install server.

PXElinux configuration

    LABEL deb
      MENU LABEL MEOW
      KERNEL vmlinuz-6.1.0-18-amd64
      INITRD initrd.img-6.1.0-18-amd64
      APPEND root=/dev/nfs nfsroot=10.141.255.254:/mnt/debian,rw  ip=dhcp auto=true noquiet nosplash

Whilst I can log in with my normal user I cannot log in with root from the console or su -, su - root I’ve reset the root password by chrooting into the filesystem on the install server. I’ve also tried adding the non-root user to the sudoers group but I get sudo: unable to open /etc/sudoers: Permission denied when I try and use it.

Can anyone give me any ideas on what to try next? debugging why root login in failing whilst not having root is quite frustrating.

The share is exported with

$ sudo exportfs -v
/mnt/debian 10.141.0.0/16(sync,wdelay,hide,sec=sys,rw,secure,root_squash,no_all_squash)

And mounted with:

10.141.255.254:/mnt/debian on / type nfs (rw,relatime,vers=3,rsize=1048576,wsize=1048576,namlen=255,hard,nolock,proto=tcp,port=2049,timeo=600,retrans=3,sec=sys,local_lock=all,addr=10.141.255.254)

Thanks!