Many users have found RJ45 anomalies with the Mac Mini M2 Pro, and Apple seems to acknowledge the issue
Brook.X
According to a discussion thread on MacRumors forum, since January 26th, some users have reported that the network on the 2023 Mac Mini M2 Pro version has a problem, specifically that when connected to the RJ45 network port, the network experiences severe packet loss.
For example, when a user tries to ping google.com, 50%~60% of packets are lost, while another PC connected to the same network cable does not encounter packet loss.
There are many user reports in the thread, and they have tried various solutions including reinstalling macOS, erasing the SSD and reinstalling, replacing the router/switch, trying a new CAT6 network cable, and restarting the router multiple times, but none of these have solved the problem.
After much testing, it seems that the issue may be a defect in the RJ45 network port, as there is no packet loss when using WiFi or a USB network card.
Two users in the thread said that they contacted Apple support and were told that the Mac Mini M2 Pro version has a defect and needs to be replaced, but the customer service did not explain the reason.
If a user needs to rely on the Mac Mini for work, they may have to find another Mac device to use while the defective device is sent in for inspection by Apple and replaced.
One user in the thread believed that this might be a software issue and found a solution by going to Settings, Network, Ethernet Interface, Details, Hardware, and changing the configuration to manual, disabling ABV/EAP mode, and changing it to "any" settings. After saving and exiting, then changing it back, the user found that the packet loss seemed to stop.
If this is a software issue, Apple could release an update to fix it. However, at the moment, Apple has not responded to the issue, so it is unclear which aspect of the problem is the cause.
