The importance of checking layer one and two

I had a simple network consisting of a Mikrotik hooked to an internet connection along with 3 APs behind it.  Nothing fancy,  The network was experiencing drop out in service.  The internet would just stop.  One of the most noticeable things would iPhones would drop the wireless link and revert back to LTE, or the internet would just stop working for them.  This was happening on a very regular basis.

Wireless testing was done, new APs were added, but no one thought to check the ports on the headend router.  Upon investigation of the logs this was found:

Normally this would be a slam dunk, however, there was nothing plugged in at all to ether4 to generate these areas.  No cable, no nothing.  If you disabled the port the errors would go away.  Re-enable the port and they would come back.  Upgrade and downgrade of the OS did not seem to fix the issue.  A new headend router was installed and everything was back to working normally.