That thread looks to be of a very similar issue. Although this was a fresh 1.2 install, rather than an upgrade.
The NIC is the same in this pc, it’s a HP machine, with a Realtek GBE FE card onboard. I have other machines (different brand) with the same card (or at least, the same model number) that boot perfectly.
I’ve just tried another identical machine, and it’s got the same issue, so it’s fault with that model of card, and not just this physical card specifically.
I’m all but a but stumped on this.
Thanks for the help so far.