@adzmedia Hi adzmedia,
I can give my nails cut for the fact that this is due to the overall slowness between the xcp-ng and XOA.
I've been having similar issue and was pulling my hair, in a usecase where my xcpng was on the other side of the VPN wire, and the virtual console of the VM, could not be drawn on time to allow me hitting any key to run the content within the mounted iso. (in my scenario I I've been using xcp-ng centre)
this issue become the relict of the past, when I did the same thing within my network (still over the vpn but utilizing a RDP of the machine within the LAN network).
maybe apache quacamole will do the trick for you, to expose some way of reching it out.
think about it.
ps. I've been having this with BIOS / UEFI, at first place I thouht this is an uefi, but it was not.