The fault was actually quite odd, it affected a third of the houses but not every third house as you'd expect, this is a short cul-de-sac so it looks like they put groups of four houses, of a total of 11, on the same phase rather than the usual every-third-house arrangement.
Anyway, thinking about this, I was wondering if anyone knows of any Internet- connected power quality monitoring gear that isn't professional-grade and therefore costs $1K and up. The closest I could find was the ACScout, but the standard USB-connected one has no online manual to see whether it could be hooked up to something like an ODroid, and the (pricey) networked ones are 110V only.
I just want voltage and frequency monitoring which will catch most things, the ACScout will alarm on over/under voltage and frequency, but that's only the non-usable net-connected ones which are 110V/60Hz. There's various plans around for using AC transformers to sample the mains signal, but I'd prefer a pre-built one rather than an ongoing science project.