The horror you do not want to see:
mount: /run/miso/sfs/livefs: can't read superblock on /dev/loop0.
dmesg(1) may have more information after failed mount system call.
I have been struggling with this and similar issues for a while now. After checking the affected ISOs, the thumb drive and all, I finally chose the nuclear option: Completely re-installing Ventoy.
Turns out this was a good call. My Ventoy thumb drive has always been updated for roughly 2 years and somewhere down the line, something did go sideways. After completely re-installing the entire drive (partitioning and all), all ISO files finally work properly now.