What were you trying to do that didn't work?
For over a year, I've been developing procedures for my team to generate pxe-bootable live images for CentOS/RHEL using livemedia-creator provided in the lorax package. The tool has worked successfully and without major issue for nearly a year on my RHEL 8-based host server running kvms for various CentOS/RHEL versions. I first encountered this issue around a month ago where the exact "livemedia-creator --make-iso ..." command would fail towards the end as it's attempting to run the following command zero empty blocks prior to mksquashfs and generating the initramfs:
fsck.ext4 -y -f -E discard /root/...img
I recall that this began around the same time of an automatic kernel update and this error began appearing in all of my kvms including the host server, but I can't be certain if this was the cause for this issue. I attempted a fresh local install of CentOS Stream 8, CentOS Linux 8.3, CentOS Stream 9, and RHEL 8.9 on a different server and am encountering the same error message. I've posted an issue prior on the lorax project on GitHub before being referred here. It might have something to do with a bad mount or user accounts and privileges, but at this point it's been really difficult to pinpoint to exact issue. 

linked GitHub issue
Please provide the package NVR for which bug is seen:
lorax-28.14.70-1.el8.x86_64
How reproducible:
CentOS Stream 8 and RHEL 8
Steps to reproduce:

1. Download and install the latest RHEL8 to server from bootable usb
   1. Basic Server with GUI
   2. custom partitioning to decrease /home/ and increase /root/
2. Login as root
3. Install lorax
4. Provide BaseOS and AppStream from same install iso on local http server (nginx)
5. Provide custom kickstart
6. Run livemedia-creator
   1. livemedia-creator --make-iso --nomacboot --ks rhel8-simple.ks --no-virt --resultdir ./results_novirt_$(date +%y%m%d%H%M)
   2. livemedia-creator --make-iso --ks rhel8-simple.ks --no-virt

Expected results
Successful generation of pxe-bootable iso files
Actual results
Problem zeroing free blocks of /root/.../lmc-disk-fzhkyrod.img