OK lets see if we can boot from a usb drive. This tutorial will instruct you on how to build a usb boot image. https://forums.fogproject.org/post/69606 the google drive link below will take you to step 7 in the thread.
https://drive.google.com/file/d/1psCrPVzBTvlakLkCMvhdoScAEZp1CKE6/view?usp=drive_link
Once you build the usb boot drive, take the kernel and init.xz from your current version of fog and replace the ones on the flash drive with the ones in from the FOG server. The files are in /var/www/html/fog/service/ipxe directory.
Once you have the usb drive ready, pxe boot into the grub menu on the flash drive, then go into debug mode. After several pages of text you need to clear with the enter key you will be dropped at a fos linux command prompt. If you can get that far then fos linux is OK and the problem is probably with ipxe or the handoff between the two.
If you want to image with the flash drive, schedule the task in the fog server BEFORE you usb boot and select option 1 from the menu. If you get it out of sequence you will get an error that says something about Null. Basically its saying you don’t have a task scheduled on the fog server so there is nothing to do. Lets see if we can get it to boot this way.