Sorry if this has been addressed before - I did look through the posts,
but couldn't see anything relevant. Also sorry if I'm missing something
obvious.

I'm trying to install chimaera on a virtualbox VM, using the netinstall
image (devuan_chimaera_4.0.0_amd64_netinstall.iso, dated Nov 18 2021) -
I've done this many times before, without a problem. This time, when I
get to "configure the packet manager", it comes back with "The
installer failed to access the mirror". I used wireshark to check that
it's talking to the network and the server - it appears to be doing so
(accessing server at 95.216.15.86).

I'm wondering if it could be another effect of the recent key expiry
problem.