Earlier today, I added a new boot image, OS image, and deployed a new task sequence for our SCCM setup. Took a UEFI laptop that previously PXE-booted successfuly, but this time nothing happened. Tried a different model, still nothing.
I mucked around with DHCP options (specifically, adding Option 60 detailed here with specific steps here). No luck. Laptop would boot up, detect media was present, then try other boot methods as nothing was found.
Started playing around with the changes I made, editing the task sequence to use an older (but still current-versioned) and it worked!
Re-examined the new boot image I uploaded and viewing Properties told me I forgot to enable PXE support on it. D’oh!