It sounds like you're talking about a USB-to-LAN adapter that is labeled as supporting "Gigabit" speeds but is actually only capable of 10/100 Mbps speeds. This can happen when manufacturers market the device in a misleading way or when there is a discrepancy between the hardware's capabilities and the specifications provided.

Here are a few things to consider:

1. Fake Gigabit USB-to-LAN Adapters: Some adapters may claim to support Gigabit speeds (1000 Mbps), but in reality, they are only capable of 100 Mbps or 10 Mbps due to cheaper or subpar hardware. If it’s marketed as a Gigabit adapter, it should support 1000 Mbps, but if you're seeing slower speeds, then it could be either a mislabeling or a lower-quality product.

2. Check the Chipset: The chipset inside the adapter plays a significant role in determining its capabilities. Some common chipsets for Gigabit adapters are from Realtek, ASIX, and others. You can look up the specific model of your adapter to find out its chipset and whether it’s capable of handling Gigabit speeds.

3. USB Port Speed: USB 2.0 ports, for example, have a maximum theoretical bandwidth of 480 Mbps, which could limit the speed even if the adapter claims Gigabit support. If you're using a USB 2.0 port, you're likely going to see speeds far below the Gigabit threshold, even if the adapter itself is capable of Gigabit speeds when used with a USB 3.0 or higher port.

4. Driver Issues: Sometimes, the drivers for the adapter may not be optimized for the specific system or operating system you're using. Make sure you're using the correct drivers that allow the device to operate at its full potential.

5. Testing Speed: You can check the actual speed you're getting by using a speed test (e.g., an online speed test or testing file transfer speeds) to compare the results with what the device is supposed to support.

If you're using this adapter and it’s not delivering the expected speeds, it might be worth considering getting a different, more reputable USB-to-LAN adapter, especially if Gigabit speeds are essential for your usage.