I've just been back on chat with Google support, and they've asked me to
make a short video of the issue and gave me a new case number to include
in the video. I then had to reply to the Email that the support person
sent me with a link to that video...
The fact that Google's own web page that details the "current" Nest
device firmware versions was "Last updated" on 6th Dec 2023 and
immediately after that a number of us with exactly the same device have
experienced this issue seems like it's firmwar...