Forgetting the network, and reconnecting did nothing. It won't stay connected for very long anymore. Probably not even a minute. Good job Apple, probably the software update broke it. Or the radio is failing.

Didn't try connecting to 2.4GHz.

Hard to believe it's the AP, my phone is connected just fine. Rebooting the AP anyways. As the problem didn't start until today, so not the day the watch was updated. Kind of sad if the AP needs to be rebooted. There's two things on the WiFi, any AP should be able to handle that, even a consumer one.

Maybe that's what I should buy, a new AP again. 2.4 GHz does it too. Looks like the watch is busted, no more WiFi on it.

Maybe rebooting the watch would fix it. If so, it might be a software problem. But if it doesn't, the radio could be busted. Resetting might fix it as well.

Rebooting the watch may have fixed it, connected for 1 minute so far. That's better then before.