I love Pi-hole, it's the kind of good software that just runs and does its thing and you tend to forget that you're even running it. But I just had a laugh as I figured out that it's the reason for a problem that has annoyed me for quite some time — though I suppose not enough to really try to debug it: the fact that my YouTube history seemed to update only intermittently.

As I just realized, by default Pi-hole blocks updates to the YouTube history (makes sense I guess), so the history was being updated when I was watching YouTube while not on my home network (eg. on cellular) — and was not being updated when I was on my home network, or away from home but VPNing home (which I often do).