Thank you all for those replies; I'll make the changes suggested. I've only just started logging with mydslwebstats, as you can see, because I wanted to track the issue in the OP. It was happening before that; at least once, maybe twice.
My location is a single residential street that goes up a hill, with little else nearby. There is nothing industrial apart from a care home and a farmhouse a bit further up the hill. I thought my cabinet was one that's about 200m down the street, I remember them putting in the FTTC cabinet some time ago. I wonder though if there's another (closer) cabinet a bit further up past my house. I don't go that way often, it's a dead-end eventually, but I'll have a look when I get chance.
My modem's a Zyxel VMG8324 in bridge mode, followed by Mikrotik RB850Gx2 Router.
The times of the events don't seem to coincide with anything in my house. Yesterday's results were remarkably close to me turning on my kit in the morning and afternoon, but off by about ten minutes so probably a coincidental red-herring. I'll continue to watch.
