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So I got a usb-c adapter/hub that gives me VGA, HDMI and some USB ports. If I connect it to one of my Pro's two ports, it works fine. If I connect it to the other, both VGA and HDMI start flickering. The port on the Mac itself is fine since I tried it with a different adapter.

Can anyone give me a hint on why such inconsistency might exist. Could it be because one port is USB 3.0 and the other is (in my understanding) USB 3.1?

Update 1: I have a Macbook Pro 13inch 2017 no touchbar and I used this dongle: https://www.amazon.com/gp/product/B0749JXV6R/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

Update 2 Just tried it with a different Macbook Pro (13inch, with touchbar), same issue persists. The hub only works with one of the ports as if the two ports are somehow different.

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    Without knowing which MacBook (Pro/Air) and what video adapter, it's going to be really difficult from this vantage point. Please update with the details of your setup. – Allan Nov 2 '17 at 22:35
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The 13" MacBook Pro has two Thunderbolt 3 ports with support for USB 3.1. USB-C is the connector type. There are no 3.0 ports at all.

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The flickering you are experiencing sounds like a clock sync issue (TDMS clock for the display, not the clock that keeps system time).

First thing I would try is rebooting with the hub/dock connected to the port that's giving you trouble. If the problem goes away, then you've narrowed down the problem.

If it remains, you may have a hardware issue. Before taking it into Apple, however, it might be a good idea to try out a different video adapter.

  • So I tried rebooting but the issue persisted. However, if I use a normal USBC to HDMI cable (from CableCreation) it just works fine. – Auxiliary Nov 2 '17 at 23:29
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    That's actually a DisplayPort to HDMI (a USB to HDMI would be an "active adapter and you would have a "box" at the HDMI end). That adapter may have an issue with the clock signal or that TB port may have an issue. I would get it checked by Apple right away while your warranty is still good. – Allan Nov 2 '17 at 23:43

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