@Sebastian-Roth Hi Sebastian, I don’t use Fog project, but i use IPXE, and encountered this very issue myself. This is on a machine with elitegroup bios, and it has 2 nics.

I noticed couple things:

1. If i open BIOS setup screen, change nothing, but “save changes and exit” i do not see this issue.
2. If i open BIOS setup screen, change nothing, but “save changes and reset”, i get exit_boot failed error.
3. If i remove the nic that’s on pci, so i only am left with the one on motherboard, I do not see this issue.

Something with the memory map & nic card & kernel is a problem.

I am using similar script to this:
https://ipxe.org/appnote/debian_live

on debian buster.

Just in case this extra info helps.