MYSTERY!!! R6900P loses ethernet connectivity. Wifi is fine.

Location: Home

Firmware Version
V1.3.2.134_10.1.66

Hi.  I am by no means a LAN expert but this is just baffling to me and above my level of comprehension.  After 5 plus years of flawless ethernet and wifi connectivity, my system crashed.  Spectrum was out and 'fixed' something on their end which got the wifi back up, but one the ethernet cable was connected to the switch (all the same equipment for 5 plus years), all hard-wired/ethernet connections fail.  I am at a complete loss as to what is causing this.

I had an IT company out and they managed to get it back up and running for a day or so.  They told me i had created a loop by using multiple switches (which makes sense but doesn't).  I have NOT reconnected anything he pointed out, but after trying to connect my security DVR directly to the main switch in the 'equipment' room, the ethernet connects are no more.

What do i need to do to figure this out?  What do i need to share for someone to help me figure this out.  I love my hard-wired devices. They have stable connectivity and reduce wifi traffic.

Thank you in advance.