Cax80 multi gig port keeps dropping connection

[VasilyB]

I have the same problem. I had to buy technical support to debug the issue. So, I had 3 calls. Right now, I am going to buy another modem from Motorola and compare results. 

Problem:
I have Comcast plan (1.2 gbps). When I replug multi-gig (2.5 gbps) ethernet port I can reach even 1.4 gbps internet but only for 10-15 min (and the multi-gig port indicator is blue). After 10-15 min it becomes white an the internet speed is 0.9 gbps.

Conversations with support:
1st call: Tried some configuration changes - no result -1h of conversations

2d call: I had to fight with the support to explain my problem... We did -reset - no result. The support suggested me to ask Comcast -90 min of conversations

- The next day Comcast technician visited my house and checked the power of the signal. The signal is perfect.

3d call: Idea of the conversation was like this: "we need more proofs". I suggested to try another modem, they confirm the idea. Yesterday I ordered another modem from Motorola to test the network. 30 min of conversations

4th call would happen after my tests.

P.S. 3 calls and no results (90$ burned).

I bought the modem last year, I still have tech. warranty. 

What doesn't work:

1. restart and reset modem

2. direct connection to the cax80 from my computer

3. playing with configuration

Question: 

So, multi-gig port indicator do not show me network speed, right? So, even I I have no internet and multi-gig port is connected to the 2.5 gbps device it should be blue, right? e.g. I have two 2.5gbps switches from SODOLA if I connect them to each other without any devices, they show me orange indicator (2.5 gbps speed between devices without the internet). I also connect 1gbps card to the switch and indicator becomes green (1gbps speed) that I expected. I wanted to test everything.. 
In one of the call with the support the told me that the multi-gig indicator has internet dependency... I think that is not correct. 

I am the big fan of the netgear... Was a big fan. I also ordered 2 more devices during the winter holidays. I am really thinking to return that back.

[FURRYe38]

What FW version is loaded on the modem? 

What brand and model device is connected to the multi gig port?

This a PC or something else? 

What CAT# LAN cables are you using? CAT6A STP is recommended for use with any 2.5Gb or higher speeds on WAN/LAN ports. 

What happens if you disable the 5Ghz radio on the modem? 

The multi gig port weather in router or modem only mode, will show WHITE, BLUE or OFF. OFF being nothing connected, WHITE for 1Gb device connections, and BLUE for 2.5Gb device connections. 

I tested my CAX80 out last year in router mode with wifi enabled and 1 ethernet connected PC connected directly to the back of the modem on the multi-gig port. All wifi running. Saw no issues. Ethernet adapter is a 2.5Gg Realtek PCI card in a Windows 10 PC. Saw another user with broadcom(?) I think had issues however after updating drivers and cabling, his remained stable at the multi gig port as well. https://community.netgear.com/t5/Cable-Modems-Routers/Re-CAX80-Multi-gig-ethernet-port-dropping/m-p/...

I believe there maybe certain devices that could be impacted or see issues with this multi-gig port. 

[VasilyB]

Router 

Hardware Version	1.01
Firmware Version	V2.1.5.2
Cable Firmware Version	V1.02.08

I have CAT8 cable, 2m lenght.

How I tested 2.5 gbps connection? 

Test 1: Using switch SODOLA 2.5 Gbps

When I connect a device to the CAX80, first 10-15 min I can see the blue multi-gig indicator on the modem and an orange indicator that shows me 2.5gpbs LAN speed. So, both of the devices (CAX80 and switch) understand that the LAN speed is 2.5 Gbps. If I check the network speed in the first 15 minutes, I can see 1.4 Gbps. So, everything is expected. After 15 min CAX80 multi-gig port becomes white and on the switch, I also see a green indicator (that shows me 1gbps speed). And when I test the internet speed it is 0.9.
I have 2 SODOLA switches: 5 and 8 ports. Both of them show me the same behavior.

Test 2: Direct connection

I have 2 Macbooks and I have a 2.5 Gbps adapter. If I connect any Mac directly to the multi-gig port directly (using an adaptor) I get Test1 results.

Test 3: Maybe I have broken switches?
I connect 2 switches to each other, without any devices or the modem. So, each switch has an orange LAN indicator (2.5gbps speed). So, that is expected. And never turned green (already 4 days passed).

Test 4: Maybe I have a broken 2.5gpbs adapter?
If I connect any of my Macbooks to any switch, the 2.5 Gbps switch indicator will never turn green. So, the LAN speed is always 2.5 Gbps.

I also tried to disable all CAX80 wifi networks - the same Test1 results.

[FURRYe38]

Is the CAT8 cable UTP or STP? STP is recommended here.

"I have 2 Macbooks and I have a 2.5 Gbps adapter. If I connect any Mac directly to the multi-gig port directly (using an adaptor) I get Test1 results." So with either of these connected directly to the 2.5Gb port on the CAX, the same thing happens after 15 minutes, the LED turns WHITE?