When I upgraded to Rawhide, netboot no longer worked and the kernel gets stuck in an endless loop, stating "__find_get_block_slow() failed" and completely funky values. It did however state that the block size was 4096 bytes. Since initrd usually uses 1024 bytes, I tried adding ramdisk_blocksize=1024 to the kernel parameters. An behold, it started to work. I leave it to you to figure out why and do the necessary tweaks. ;)
*** Bug 219511 has been marked as a duplicate of this bug. ***
fixed in 0.1.42