Why is my wireless LAN suddenly transferring files so slowly?

[Paladin]

@continuum I'll have to try that on the other machine (the one depending on wifi). On this one connected by ethernet cable to the router the Speedtest.net results are 658+ Mbps down and 42+ up.

I looked into downloading a new driver. The model of wireless adapter is a TP-Link Archer T4U Plus and does support Wireless AC after all. I found a new driver but it looks like it's using a much more recent Realtek one.

But after all is said and done I feel totally silly, because it turns out the stupid thing had at some point connected automatically to the 2.4 GHz band and not to the 5 GHz one. I corrected that and configured it so it wouldn't connect automatically to the 2.4 GHz band.

That happens if you wander out of the effective 5Ghz range (which is much smaller than 2.4Ghz) or if something interferes or blocks the 5Ghz signal. Could be as simple as someone standing too close to one PC or the other, or near the router for a while, or moving a piece of furniture, putting something next to the router, bumping the antenna on the PC or router, etc. Wifi can be fragile.

 

[Paladin]

I would check for a driver and firmware update for the WiFi hardware.

 

[Paladin]

That might help, it is probably using the default one from Windows. You never know if the original one might work better.