@leviathan Well the easy part, is FOG doesn’t support 22.04 yet. I would stick with ubuntu 20.04 for now. Being on the branch version is the right place to be
You also need to make sure you setup things in the right order.
FOG 1.5.9.115, then update the FOS Linux kernel to 5.15.x series, then recompile ipxe.
Your problem here is when iPXE fails to transfer all of the FOS Linux image (bzImage and init.xz) the problem is either you have an old version of iPXE or you nave network communication issues.