Purely by coincidence, I found the solution to my problems.
Well, half a solution.
My new laptop doesn’t have an HDMI port, so I bought myself a “Verbatim Multiport” from digitec for 46 CHF. This has an RJ45 socket built-in, so now my laptop is connected via a cable, rather than Wifi, and it’s back upto full speed and is stable.
So, it’s actually the Wifi which is the problem in these UPC boxes.
Even last night, my laptop had perfect connectivity, but my daughters were complaining as their smartphones were connected to my UPC Wifi, but their phones were saying that there was no internet.
Oh, and to say it again… my laptop was always sat on my desk, 15cm away from the UPC router. My original problem was not caused by it being too far away, or having a brick wall between it and the router.
The UPC router’s Wifi itself is just not stable.
Much like the UPC TV box….
One other quirk of the unstable Wifi… my printer is only connected via Wifi. Usually, I’ll print things out and it’ll start printing straightaway. Other times, I’ll try and print…. and it’ll only start printing 1 or 2 hours later. My (cable) internet is fine… but the Wifi is just flakey.