@Sebastian Roth Our client machines range from Dell Optiplex 7040s to 7060s. It times out for all models, just not working period. Running FOG version 1.5.4. DHCP server is Windows 2012 R2. PXE booting legacy BIOS clients work, and I’ve made the necessary changes according to this:
https://wiki.fogproject.org/wiki/index.php/BIOS_and_UEFI_Co-Existence#Using_Windows_Server_2012_.28R1_and_later.29_DHCP_Policy

UEFI PXE boot doesn’t through network, only with USB flash drive. PXE over IPv4 times out.