Hi Balder, you have to provide more details. I guess you have upgraded your FAI versions from buster to bookworm. Is that on your own FAI server? Did you recreated the nfsroot? Did you checked the logs of the build process (fai-make-nfsroot) and checked which FAI and which dracut versions are used inside the nfsroot?
Do you boot your clients via network or via ISO using a squash.img? If the installation aborts, try to save the log file /tmp/fai/fai.log and upload it to paste.debian.net so we can have a look at it. -- best regards Thomas