@SteveMann 

Hey

Could you post a picture of what you are seeing?    But if it is what i think it is, namely a WIFI type symbol near its name on the device list.. then yes its connected via MESH.. Opening the device should tell you how its connected, ROOT AP etc. 

You could first try disabling MESH and see if it forces it back online, had this happen due to a 10mbps connection to the AP so the controller decided (correctly) that WiFi Mesh would be faster.

If it goes offline totally after disabling MESH, then its likely a cable issue, obviously give it 2-3 mins to re-adopt itself just to be sure.

  @SteveMann 
Thanks for the reply. You surmise correctly that it is the WiFi symbol next to "Connected".

But, this morning the WiFi symbol is gone and everything appears to be working.

Your reply makes sense as the cable from the AP to the switch is the most questionable of all because it goes through two patch panels.  I will plan on a day to pull a single cable from the switch to the AP.

But, I was under the impression that I had to specifically enable mesh?

  @SteveMann 

I cant remember if Mesh is on by default or not, either way it looks to be enabled on your setup.  See below of what I am seeing

If you got to that location you can disable MESH

Also check the wired link on your AP, that might give you some info to work with.  As metioned i had a customer that kept going mesh, during mesh times it was reading as 10mbps in here so cable was the root cause.