This morning after being on the internet on my tablet for a while, the internet dropped. Not unusual, except it wouldn't come back (wifi was still live). Then I discovered my pc, on the same switch as the wifi router, also wouldn't connect (that is unusual). MrsD.'s pc (directly connected to the DSL modem) OTOH has no internet issues. WTF? I decided try the modem's dodgy-at-best wifi. I flipped it over to copy the wifi password, then when I went to connect my tablet, the usual internet connection came back up solid on both my tablet and pc. Guessing some sort of cabling issue, except there was no physical disturbance to cause it. The ~40-ft ethermet cable connecting the modem to the other wifi router and my pc via a switch is old AF.
I've had switches, well, two switches, lose individual ports. One then went on to fail completely. The other stayed working on the other ports until I replaced it. In both cases there was no warning, it just happened. I'd suspect whichever switch you're plugged into.
IIRC they were both cheapish Netgear things, little white boxes, 5 port. Can't remember if they were both gigabit, but the second one was. I have a better 16 port Zyxel thing now with everything for the house going through it, except the wifi which has access points connected to the main router which hangs off the fibre ONT on the wall.