In our new office all of our ethernet jacks are "double jacks" (two ethernet ports on one plate on the wall 
), each with their own CAT6 cable wired to a series of identical dual jacks (we didn't have time to order a patch panel) near the switch. We then use CAT5e cables to connect devices to the jacks on one end and the jacks to the switch on the other end.
We just plugged in a Samsung SCX-4848FN printer/scanner to one of the jacks and it works fine. However, the computer (WIN10 Pro) plugged into the jack next to it is suddenly losing connectivity (when we turn of the printer the problem goes away). The network interface shows as connected, but the machine cannot even ping the default gateway (which is a pfSense router plugged into the switch). Both machines are receiving different static IP assignments over DHCP from the router and the MAC addresses are different. The problem is resolved by disabling and re-enabling the network interface on the windows machine.
Could the problem possibly be caused by interference from the two network jacks next to each other (we have not yet had the ability to see what happens if we plug the printer into a jack located elsewhere)? If not, what else could possibly be causing this?
The only other thing I can think of is that when the guy wired the wall jacks, he wound the slack in the cables around the ports before securing the lid in the panel. I don't know if that would cause interference between the two cables…
Best Answer
I would bet on shitty installation causing reduced signal quality and interference between the two ports. Cheap cable testers will tell you if a wire is open-circuit or connected to the wrong pin but won't really tell you anything beyond that.
The first thing I would do is unscrew the ports and inspect the terminations. If you see large amounts of untwisted wire then cut it off and re-terminate with the minimum possible amount of untwisting.
If you are still having problems then IMO it's time to call in a professional network installation firm who can test the work with high-end test gear and if needed re-do it.