Ethernet Port Issue

> I had initially thought this was a poor cable somewhere [...]

   You may have been right.

> [...] However, [...]

   Any hardware change could affect some marginal condition in other
hardware -- flakey cable, weak receiver/transmitter, ...  One device
might erroneously negotiate a 1000MHz link, and then fail when it tries
actual communication at that speed, while another device might fail to
negotiate a 1000MHz link, and then work better at a lower speed.

> [...] Connection speed is ~90mbps which is below the gig speed, [...]

   Gigabit speed uses all four pairs in a cable; slower speeds use only
two.  On the Mac, System Preferences > Network : Ethernet <n> >
Advanced... : Hardware should tell you the physical link speed.

> [...] trying to figure out how to access via the switch only (no AP
> between device and switch).

   I'd try to move the computer to within range of a known-good cable,
and, if that works, then start adding questionable hardware until the
failure (re)appears.

   I recently spent far too much time on the phone with a friend whose
Windows system seemed to be confused about the existence of his
Ethernet/Internet connection.  LEDs were flashing happily everywhere,

but the Internet was always out of reach.  In desperation, he hauled the
computer to within different-cable-range of the network switch, swapped

cables, and every ill was instantly cured.