Netgear GS748Tv6 port issues

These built-in cable test feature results depend on many different factors - on the effective used cable, cable length, on the installation, on the connected device, on shielding, on grounding, .... This "feature" - regardless of the brand model of the switch - does not, Not, NOT replace a high quality cable measurement tool. Needless to say, these measurement tools always come with a tester -and- a plug for the other end to return some meaningful -measurements-. 

Built-in Cable Tester | NETGEAR Communities 

https://www.netgear.com/hub/business/av/poe-cable-length-standards/ 

https://kb.netgear.com/29789/How-to-use-the-Cable-Tester-feature-on-NETGEAR-ProSAFE-Click-Switches

Important note:

The cable diagnostic utility in the device might yield different results. It can be due to a variety of factors, from link speed (10/100/1000) or cable types (Cat5, 5e, 6, 7, STP, UTP, etc). This is generally due to the electric signal changes based on those factors. Since the switch is a gigabit switch, it is recommended to use CAT5e STP cable, or better, and a gigabit link partner.

Kmiller0526 wrote:

Obviously, it sounds like a bad port on this brand-new switch,

Extreme unlikely.

Kmiller0526 wrote:

We have some Linux servers connected to this switch, so doing the cable test messes with them.

Let me guess: Affected are (hard to imagine it should be a Linux thing...) faster MultiGig, 10G, or faster Ethernet ports, PoE-powered adapters, ...  Provide more details, like make, model, version of the Ethernet adapter, please.