@JeffBerntsen I tried it with nothing plugged in, also disabled extra settings in the BIOS, unneeded hardware, Atom cores, Hyperthreading etc, everything but 2 CPU cores and nothing made a difference. What did finally work was re-installing with the 'no serial' option and everything seems to be working as expected now. I only have a handful of XCP-NG installations under my belt but I wonder if this is a known bug or if anyone else has had a similar experience.

@JeffBerntsen no KVM - monitor, kb, mouse directly connected. I did also unplug all 3 and booted up but it didn't change anything, after waiting a few minutes I plugged the keyboard back in and had to make a selection to get it to load XCP-NG.

@Danp

[15:31 XCP-HV ~]# cat /boot/efi/EFI/xenserver/grub.cfg
serial --unit=0 --speed=115200
terminal_input serial console
terminal_output serial console
set default=0
set timeout=5
menuentry 'XCP-ng' {
search --label --set root root-dpefle
multiboot2 /boot/xen.gz dom0_mem=1424M,max:1424M watchdog ucode=scan dom0_max_vcpus=1-4 crashkernel=256M,below=4G console=vga vga=mode-0x0311
module2 /boot/vmlinuz-4.19-xen root=LABEL=root-dpefle ro nolvm hpet=disable console=hvc0 console=tty0 quiet vga=785 splash plymouth.ignore-serial-consoles
module2 /boot/initrd-4.19-xen.img
}
menuentry 'XCP-ng (Serial)' {
search --label --set root root-dpefle
multiboot2 /boot/xen.gz com1=115200,8n1 console=com1,vga dom0_mem=1424M,max:1424M watchdog ucode=scan dom0_max_vcpus=1-4 crashkernel=256M,below=4G
module2 /boot/vmlinuz-4.19-xen root=LABEL=root-dpefle ro nolvm hpet=disable console=tty0 console=hvc0
module2 /boot/initrd-4.19-xen.img
}
menuentry 'XCP-ng in Safe Mode' {
search --label --set root root-dpefle
multiboot2 /boot/xen.gz nosmp noreboot noirqbalance no-mce no-bootscrub no-numa no-hap no-mmcfg max_cstate=0 nmi=ignore allow_unsafe dom0_mem=1424M,max:1424M com1=115200,8n1 console=com1,vga
module2 /boot/vmlinuz-4.19-xen earlyprintk=xen root=LABEL=root-dpefle ro nolvm hpet=disable console=tty0 console=hvc0
module2 /boot/initrd-4.19-xen.img
}
menuentry 'XCP-ng (Xen 4.13.5 / Linux 4.19.0+1)' {
search --label --set root root-dpefle
multiboot2 /boot/xen-fallback.gz dom0_mem=1424M,max:1424M watchdog ucode=scan dom0_max_vcpus=1-4 crashkernel=256M,below=4G
module2 /boot/vmlinuz-fallback root=LABEL=root-dpefle ro nolvm hpet=disable console=hvc0 console=tty0
module2 /boot/initrd-fallback.img
}
menuentry 'XCP-ng (Serial, Xen 4.13.5 / Linux 4.19.0+1)' {
search --label --set root root-dpefle
multiboot2 /boot/xen-fallback.gz com1=115200,8n1 console=com1,vga dom0_mem=1424M,max:1424M watchdog ucode=scan dom0_max_vcpus=1-4 crashkernel=256M,below=4G
module2 /boot/vmlinuz-fallback root=LABEL=root-dpefle ro nolvm hpet=disable console=tty0 console=hvc0
module2 /boot/initrd-fallback.img
}
[23:32 XCP-HV ~]#

I have tried fresh installs of 8.2.1 and 8.3 and it will boot but not until I select an option from the GRUB menu. I am using UEFI without secure boot. There is an asterisk next to the 'XCP-NG" option which I believe confirms it is the default option, but GRUB will not start it until I manually select it. I'm a Linux novice and have not had success trying to edit the GRUB config file using methods I've seen elsewhere online. How does XCP-NG set the GRUB timeout value?