Stable for a year, now stuck at 90 Mbps after connection drops

[danieloverton84]

Hi all,

I have Sky FTTH 500 Mbps which has been in for about a year. It was installed in November 2024 and has been flawless up until recently. I’ve never used the Sky Hub. From day one I connected my Unifi Dream Machine directly to the ONT’s Ethernet port and it has always worked perfectly.

Over the last few weeks I have noticed that speeds have dropped significantly. The Dream Machine runs a scheduled speed test every day at 4am. The results used to be a consistent 500 Mbps down and around 70 Mbps up. Now the logs show that whenever the WAN connection blips, the downstream speed drops to about 90 Mbps while the upload remains at 70 Mbps.

If I restart the ONT, speeds immediately return to 500/70, but only for a limited time. Sometimes the full speed lasts a few minutes, sometimes several hours, and once it held for nearly a full day. After the next set of WAN drops, it goes straight back to roughly 90/70.

Speed tests have been run both from the Dream Machine and over Ethernet using speedtest.net, and the results match.

Has anyone seen this before? What could be causing the downstream to cap at around 90 Mbps after WAN interruptions, only to be restored with an ONT reboot?

Any thoughts would be appreciated.

[Chrisee · Accepted solution]

@danieloverton84 cannot think of a fault with those symptoms. Unfortunstely Sky will not investigate while you are not using the Sky hub as their own tests require a hub to be inplace.

One thought as 90Mb/s would be the speed delivered over a 100Mb/s Ethernet link as opposed to a gigabit link I would change the Ethernet cable connecting the router to the ONT as if there is a small break in ine of the 8 connectors could cause the speed to intermittently revert to 100Mb/s. 

[JimM1]

@danieloverton84 Not sure if your Router has the indication software wise, the Asus does and indicates the Port status as connection speed, orange / green where 100/1000Mb/s state is displayed, got on Samsung TV on one off the mesh unit's that has a 100Mb/s NIC on it so port is Orange. May be a way for you to see if that is possible!

[danieloverton84]

You might have hit the nail on the head with this answer. After I read your reply it makes total sense so I plugged another cable between the two before lunch yesterday and so far its held speed. 

[Chrisee]

@danieloverton84 happy to help.