Never mind, I figured it out: My TP-Link switch apparently will "lock out" a port for some unknown reason, disabling it until I physically power-cycle the Switch (pull the plug and reconnect.) After I did that, the dead port came back to life. Soft rebooting the switch through the management app did NOT do the job, i had to power the unit dow. Does anyone know why this happens, and how I can prevent it from happening again? And why the heck the management app doesn't indicate that a port is in this condition?

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For the second time, with a different device, I am experiencing no IP when connected directly to the switch (either of two different ports), BUT, I get a connection just fine through a cascaded unmanaged switch, or even double-cascaded switches. The Monitor function in the management app shows 0 transmitted packets to that port, though some received. I've tried changing the settings for the port, to no avail (reverting to the normal setting). I've tried rebooting the switch, as well as my router. The cable test reports a normal, 1-M cable. How the heck can the device work fine if I insert a second switch after the TP-Link, but not when connected directly? I'm stumped. If anyone has any insights, please chime in.