I know this is old but just ran into this. It's actually not a defective drive (most likely). It is the cable cables in the 2m length range will slow down to USB 2 speed (480 mb/s). If you are using an Apple USB charge cable it even mentions this here (https://support.apple.com/en-us/HT208368) at the bottom. I tried a USB 3 to USB C (plugged into a USB C adapter) and speeds went back up to around 500 mb/s from the 40 mb/s i was getting originally. Just food for thought.
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