Yeah, all up to date.
PC is wired (can you imagine!) 
Not that I'm old school (although I am) it's because this machine has two gigabit ports and the WiFi is on USB so it's a bit pointless.
I have no real reason to suspect the Pi or PiHole since all the other machines (all wireless to be fair) are working as advertised. I'll hook up the spare Pi3 to a wired outlet just to isolate that.
EDIT: tried on the Pi 3 (Firefox ESR) and sure enough - PiHoled.
Tried a domain I never heard of (blacklisted it first) completely unaffected. D*** you Windows... Or something.