@Acuity From what I know about this and read between the lines I think this is caused by the Dell Optiplex AIO 5270’s UEFI firmware not being able to find EFI boot loaders by itself. We had other people report this kind of thing and I thought about adding a feature to FOG that would also save a copy of the EFI boot entry with the image and also deploy it to new machines (forum topic). While it seems to be a vital thing to do on first sight I stepped back from the idea because we don’t have many reports on this being an issue at all (1, 2). While on the other hand we have reports on UEFI firmware creating multiple boot entries (new one on every deploy I guess) or somehow messing with the entries by themselves (1, 2) Because of that I decided to better not mess with the EFI boot loader entries as it could cause trouble on systems we don’t know well enough (like dual boot and such).
Nevertheless you can try to use efibootmgr tool in post deploy scripts to set the boot entry for you. Search the forums for those two things and if you need assistance just let us know.