After buying a MacBook Air with an M2 chip, I connected it to an external monitor along with another Dell laptop and switched between them using HDMI and USB-C Ethernet hardware. The HDMI switch worked well, but the internet connection was not stable. At first, I did not suspect the USB-C Ethernet adapter because the connection appeared normal most of the time.
The problem was intermittent: pages would stop loading, the Mac would recover, and then everything looked fine again. That made it hard to tell whether the issue was my ISP, the router, macOS, the Ethernet cable, or the network adapter.
I used UptimeLog to keep a history of when the internet connection went down and how long each interruption lasted. The goal was not to prove the adapter was guilty immediately, but to track the connection drops clearly enough to compare different hardware setups.
Symptoms I was seeing
The Mac Ethernet connection was unstable, but not in an obvious way. The connection would work, then briefly drop, then recover. Because the drops were short, it was easy to miss them unless I was actively using the internet at that moment.
This is what made the USB Ethernet adapter difficult to diagnose. If a USB-C Ethernet adapter keeps disconnecting on a Mac only once in a while, the issue can look like a general ISP problem instead of a local hardware problem.
How I tracked the connection drops
I let UptimeLog run in the background while I used the Mac normally. It recorded when the internet connection went down, when it recovered, and how long each interruption lasted. That gave me an internet connection history instead of relying on memory.
If you need to monitor internet outages on a Mac, this kind of history is useful because it separates “the internet felt unreliable” from actual timestamps and outage durations.
Why the Ethernet adapter was suspicious
Once I had a record of the connection drops, I could compare what was connected at the time. The interruptions appeared while using the USB-C Ethernet setup. That did not automatically prove the adapter was responsible, but it made the adapter suspicious enough to test directly.
The important clue was that the Mac internet disconnects were not constant. They were intermittent, which is exactly the kind of behavior that can happen with a flaky Ethernet adapter, cable, hub, or USB-C port.
Testing another adapter
To isolate the problem, I tested the Mac with a different network path instead of assuming the ISP was at fault. If you have another USB Ethernet adapter, another USB-C port, or a way to compare Wi-Fi vs Ethernet, that comparison can be more useful than staring at a router status page.
When testing, change one thing at a time. For example, keep the same Ethernet cable and change only the adapter, or keep the same adapter and change only the USB-C port. Then keep monitoring long enough to see whether the connection drops return.
What fixed the problem
In my case, the evidence pointed toward the adapter setup rather than a broad ISP outage. Replacing or avoiding the suspicious adapter path made the connection stable again. I would still describe this as a practical diagnosis rather than absolute proof: the pattern changed when the adapter setup changed.
That was enough to stop treating the issue as a mysterious internet problem and start treating it as a local hardware problem.
How to troubleshoot a similar issue
If your USB-C Ethernet keeps disconnecting on a Mac, these checks can help narrow it down:
Try another Ethernet cable. A loose or damaged cable can cause intermittent internet connection drops that look like adapter failures.
Try another USB-C port. If Ethernet disconnects only on one port, the port, hub, or physical connection may be part of the issue.
Try another Ethernet adapter. If the connection becomes stable with a different adapter, the original network adapter is a stronger suspect.
Compare Wi-Fi vs Ethernet behavior. If Wi-Fi stays stable while Ethernet drops connection on the Mac, focus on the Ethernet cable, adapter, hub, or port.
Check whether outages occur only while using the adapter. If the same drops happen on Wi-Fi and Ethernet, the issue may be upstream, such as the router or ISP.
Consider sleep and network switching. If the Mac sleeps, wakes, or changes network interfaces, those events can look like connection interruptions in your history.
Use a continuous ping, router logs, or a monitoring tool. The key is to collect timestamps so you can compare outages against cable, port, adapter, and network changes.
What UptimeLog helped with
UptimeLog did not magically identify the adapter by itself. What it did was keep a clear record of internet downtime, connection drops, and recovery times. That made it easier to compare one setup against another and notice that the problem followed the adapter path.
For intermittent issues, that history matters. Without it, short outages are easy to forget or misattribute.
When to replace the adapter
If the drops stop when you use another adapter, cable, or port, then replacing the adapter may be the simplest fix. If the drops continue across all network paths, keep looking at the router, ISP, DNS, VPN, or other parts of the connection.