Connected No internet (downstream at WAP)

Every once in a while, we would see on our devices "connected, no internet" and a reboot would always correct it. That said, I have a shielded, buried cable connected to the router that terminates to a TP Link that has always worked, with the only problem is getting the same error. But once again, at a Windows desktop that utilizes the TP Link WAP, the "connected, no internet" is observed. I have rebooted the router, the WAP, the desktop several times. All the while we do not see the error 'upstream'. The WAP indicates everything is working (pwr, 2.4, 5) except for the internet. 

Any advice?