Need Help: Ethernet pre-wired home not working... almost...

I have in-wall Ethernet wired in my home. All the wires consolidate in the shelf in the closet behind an electrical box. I know it's one of the worse places for a wireless router to be, but I'm stuck with how it's wired. So here's my situation.

When I plug all the cable into my Netgear R7000 Nighthawk AC router, all the Ethernet ports in my home work and doesn't have a problem getting a connection. Since I have a few spare Linksys WRT54G routers laying around, I decided to stick it there and use it as a switch. None of the ports work when I do. One of the ports does try to negotiate a connection before giving up when I plug a laptop to it, but ultimately, still doesn't work. The old Linksys is configured properly and works seamlessly when tested with some spare 10 meter Ethernet cables in the same network configuration.

I thought maybe my in-wall Ethernet works with my Netgear Nighthawk and not my old Linksys because it has gigabit ports, so I went out and bought a TP-Link 5-port unmanaged gigabit switch. When I went ahead and wired my in-wall Ethernet to it, same issues as the Linksys. Just doesn't work. Again, I tested the new switch I bought with spare cat 5e laying around and connected it to my router to test it and it works as it should.

Does anyone know how to resolve my issues and get my in-wall Ethernet to function properly? Placing my primary router there severely degrades my wireless signal which is something I'm avoiding. The Netgear Nighthawk is expensive and don't want to purchase another one just to use as a switch. Preferably, I wouldn't want to purchase anything else as I've already wasted money on a switch.

My guess is at there may be voltage drops or line interference in the cabling. But if that's the case, why does my Netgear work and not my switch or old Linksys?

I did try to use a Powerline 500mbit adapter from cable junction, but still can't get a connection at the other end of the port. Leaving the Powerline adapter in the same outlet, I plugged my laptop to it directly to test the connection and again, it works. I'm not sure why the in-wall Ethernet is so fickle, but I hope someone can shed some light on this issue.

I'm not sure what the length of the cabling is, since the house was pre-wired and don't know the exact details on where they run. It is category 5e though from insulation jacket. Both my Linksys WRT54G and Netgear R7000 are running DD-WRT firmware.