Asus RT-AX86U slow download speeds

[GW4C]

I've had this router (Asus RT-AX86U) for a little over two years and it has functioned perfectly until this last month. I have 2gig symmetrical fiber internet and when using the router's built in speed test, I was getting ~1,800mbps download and ~2,000mbps upload until mid-March. For the past couple of weeks, the speed test is showing ~400mbps download and ~2,000mbps upload. I have no idea why the download speeds are so slow. A technician from the internet provider stopped by and confirmed that the ONT is flashing a green light which means that the receiving client (my router) is sub gig. They connect the ONT to two different routers they brought with them and both of them were showing ~2,000mbps download speeds. So it has to be the router. Does anyone have suggestions on what I can do to troubleshoot this issue?

Some additional details:

• The ONT is connected via Cat5E cable to the router's 2.5gb wan port.
• The router firmware version is 3.0.0.4.388_24231
• I have tried rebooting the router and ONT.
• I have not tried to factory reset the router.

 

[bbunge]

Cat 5e should work unless it is too long. Try a new cable? What does the router show for connection speed for the 2.5 gb port? Reset with initialize may help.
I returned an AX86U under warranty that was acting goofy. Asus said it was a bad power connection and sent another router...right...

 

[GW4C]

The 5e cable is approximately 6 feet long. It has worked for the last two years. It's only been in the last two weeks that the download speeds dropped. Two things: if it was a cable issue, wouldn't the upload speeds also be affected? And the tech who came over today attached their own router to my 5e cable and it pulled ~2,000mbps download and upload speeds without issue. The problem definitely seems to be with my router. Do you happen to know where I can find info on the connection speed of the 2.5gb port? I might just end up using my credit card's extended warranty service to replace it. Do you happen to know how long the warranty period is for these routers?

 

[GW4C]

Cat 5e should work unless it is too long. Try a new cable? What does the router show for connection speed for the 2.5 gb port? Reset with initialize may help.
I returned an AX86U under warranty that was acting goofy. Asus said it was a bad power connection and sent another router...right...

I ended up factory restoring the router first and setting it up as a brand new device. Still unfortunately received the same slow download speeds. I then tried to reset the router and import my prior settings. The same issue still occurred. I'm thinking that it may be a component failure, so I've ordered a new RT-AX86U Pro and Amazon will deliver it tomorrow morning. We'll see if that resolves the issue. If not, I'm truly perplexed on what the issue may be. The two non-Asus routers that the internet provider tech used today connected via my cat5e cable pulled 2gig symmetrical speeds without any issue.

 

[bbunge]

Warranty depends upon where you live. In the US it was two years.
Port status is in two places: Network Map/System Status/Status or AiMesh/Network.
If you registered the router with Asus when you bought it, log into Asus Support and check if it is still under warranty. If it is, get an RMA to send it in. It makes a great AiMesh node.