help Ethernet connection set it's self to 100mbps... HELP

[Madders]

So randomly yesterday my PC decided to limit my download speeds to 100mbps up, and down. I don't know why and I thought it was the cable so I replaced the cable, still not fixed. I plugged the new cable into another device and it gave internet speeds I was expecting.

 

I then thought "okay, it's probably dirty contact pins in the 2.5gig ethernet slot" so I cleaned it out with isopropyl alcohol and a cotton wool bud, waited for it to dry and still no change after all that.

 

I then thought it was most likely a windows setting that had randomly enabled it's self that I can't find, and I mean I looked everywhere. I tried changing the Speed & Duplex to "Auto Negotiation" but I realised that was already set properly. I tried updating drivers, nothing. I tried unplugging the ethernet and plugging it back in to see if that's the issue, no luck. I came across something in task managers "network details" tab however that seems to be my problem, there's an image attached showing it but it seems the 100gbps or 1gbps has been disconnected and the 100mbps has connected it's self randomly. Does anyone know the solution to changing this?

 

Edit:
While doing a test on fast.com, the internet was at 100mbps and then suddenly jumped to 700mbps at the end of the test, then back down again when re-testing. I don't have any idea what could cause this when it's clearly limited to 100 mbps
 

Edited March 26 by Madders
Added information

[mattrulz12]

If you set Speed & Duplex to 2.5GB Full duplex in device manager, what happens?

[Madders]

On 3/26/2024 at 6:14 PM, mattrulz12 said:

If you set Speed & Duplex to 2.5GB Full duplex in device manager, what happens?

Sorry for the late response, it doesn't change it. It's still capped at 100/100

[AI_Must_Di3]

That sounds like your isp may be throttling you for going over the "unlimited" wall. Do you have more than one ethernet port on the mobo? Sometimes they come with two different ethernet ports.