WinPE Network Boot fails, but ISO boot working

[jpwise]

I've run into some issues over time as well. Strip back the config to a known good PE image. ie; the base ADK PE WIM file, and see if it can boot that.
If it boots that, the issue is specific to the WIM file. I do also recall some issues around the BCD and how large a ramdisk it supports, but it's been a couple of years since I set our config up, so that's off the top of my head.
If your PE image is particularly large it may be a sizing issue, and using the original stock PE base should help isolate the issue for test purposes.

It's a few pointers to check anyway.

Jp.