Okay, I really should avoid doing this stuff when I’m a little tired, as it leads to doing totally stupid stuff. Like completely missing out the git pull and blanking on that fact no matter how many times you look 
!
I wondered briefly if there could be something odd with the deprecated alt-logo theme component (which I forked just before the max-version was committed, since I still have to use it), but thankfully not.
Sorry to have bothered you for something so silly & obvious!