cannot get 2025 ISO to boot in a gen2 VM (but can in a gen1)

[KK20]

This is an odd error.  On an old r740 intel server there are no issues with creating a VM for server 2025 (and W11 ISO coincidentally).  Boots just fine from the ISO downloaded from Microsoft.  On my EPYC server I can install any other gen2 ISO but NOT server 2025 or W11 - neither will boot from iso - a boot loop "press any key" followed by a brief loading then reset.   I thought I would be clever and install a gen 2 2025 (and W11) then move  (with shield certificates already on each machine as i've moved TPM VMs before) from the old r740 to the EPYC but this wont boot either!  The funny thing?  I can create a gen1 VM, enable "key storage drive" etc and proceed to boot the W11 or 2025 ISO without issue.  It is only on Gen 2 that I cannot boot (either ISO or a fully "moved working 2025 VM".

 

Tried with secure boot on/off.  TPM on/off (yes I know TPM is required but for testing tried with off).  

 

The EPYC is a datacenter 2022 OS hypervisor and has been running 2022 VMs, Ubuntu server, and an older 2016 VM (which WAS going to get migrated to 2025 hence the test) for a year without issue so no idea what is going on here.  Has anyone else had any similar issues? 

[KK20]

ok so UNTICKING "migrate to a physical computer with a different processor version" lets me install either in a gen2 (Gen1 is happy to leave this ticked).  This wont be a problem for me but this is definitely odd.   I have always been conditioned into ticking this as I used to have a slightly different CPU in an older cluster (so needed to check this for live migration).