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I have a 2016 15" Intel MacBook Pro (4-port USB-C) that's still kicking, but I just noticed some very unusual behavior on one of the USB-C ports (the top right). For some reason, when used with a particular USB-C flash drive (the 64GB variant of this one: https://www.kingston.com/en/usb-flash-drives/datatraveler-microduo-3c-g3), the drive only works in one orientation (upside down).

I can not explain it.

  • This flash drive works in every other USB-C port in both orientations.

  • Other flash drives work in the top right port in both orientations.

  • USB-C PD works on the top right in both orientations.

  • USB-C hubs work on the top right in both orientations.

  • Powered USB-C devices, like 2.5" HDD's work on the top right port in both orientations.

  • The specific flash drive I'm seeing this issue with is the 64GB model. However, I have an older sample of the 128GB variant of this exact drive and it works in both orientations.

  • I have three of the 64GB model, and they all exhibit the same behavior—they work on the other three ports in both orientations, but only work on the top right port in a single orientation (upside down). Da fuq?!

I have reset SMC and NVRAM/PRAM. I can not explain this absolutely bizarre behavior. I can't even come up with a possible cause. Everything seems to work just fine, except when you plug this particular flash drive in to the top right port nothing happens—it doesn't mount or show up in System Information or anything—unless it's upside down, and then it works as expected.

Any ideas?

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It seems likely that there's some mechanical explanation. Perhaps the 64 GB model of that flash drive has a USB-C plug that is ever so slightly out of spec - and your top right USB-C connector on your MacBook is ever so slightly worn or deformed in just the "right" place - and together that means that the necessary connections are not made when the drive is inserted in that specific orientation.

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  • The two connectors on the Mac and the flash drive are quite literally the only real “wear” components save for the hinges and key mechanisms. A 7 year old device is going to show some wear.
    – Allan
    Aug 25, 2023 at 22:18
  • We've noticed on literally of hundreds of 2-port MacBooks that users unconsciously use the same port for charging and data transport (storage device/AV connection) while the other port is relatively unused. In our case, our users plug/unplug from classroom USBC AV cables multiple times a day for projectors and charging, and their 'preferred' port becomes physically wonky over time. This can cause charging and AV problems, as well as external device glitches. If you've used the upper-right port as the default port in most cases since '15, Bob's your uncle.
    – IconDaemon
    Aug 25, 2023 at 22:29
  • What's a good way to test this? I have a USB-C pin tester for cables, but I'm not sure how to test a powered port. Aug 27, 2023 at 0:08

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