I have a 2017 MacBook Pro. It has 2 USB-C ports on the left side and I use an Aukey hub to provide more ports (4 USB, 1 HDMI, 1 USB-C) and always to connect two monitors.

I connect one monitor through the hub with the HDMI port and another directly to the MBP with a USB-C adapter. Sometimes when I connect the hub to the Mac and the 2nd monitor to the Mac, it works as it should with no problem...but more than half the time I have to connect, disconnect, jiggle, jangle, switch ports, reconnect HDMI, etc. and hopefully they will both work. OFTEN, I can only get one monitor to fire up.

Is there any kind of software fix or reset that might solve this issue? Any other thoughts welcome. Thanks.

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    Sometimes I connect.... To what, exactly? Is it the monitor? Random peripherals? The whole hub? Please clarify what exactly is not connecting as you expect. – Allan Mar 19 '19 at 14:35
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    It is more than likely the Aukey hub which is causing the problem. Since the introduction of USBC-only Apple laptops, at my school we've been testing many different adapters and hubs and found many to be lacking either in construction, operation or both. I personally use a SIIG USB C Mini Docking Station for my 2018 MBA and it is a solid device. SIIG offers six versions of this station, too. Disclaimer: satisfied user of SIIG products. No financial or other consideration given for this recommendation. – IconDaemon Mar 19 '19 at 14:45
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    There's a very good chance it's the Aukey hub as @IconDaemon describes , but specifically, the Aukey hub is most likely a passive HDMI adapter. You need an active HDMI adapter or better yet, don't convert from DisplayPort if possible (use the DP port on your monitor if available) – Allan Mar 19 '19 at 14:48
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    It's probably not an active adapter. Try rebooting with everything connected and see if the monitor comes up... – Allan Mar 22 '19 at 15:03
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    I'll write up an answer for you.... – Allan Mar 22 '19 at 15:16

It's not a software fix, but a "hardware" one, that will address this issue.

The problem lies in the fact that the multi-function hub most likely doesn't supply an active HDMI adapter. You can usually get around this limitation with a reboot, but that can become burdensome especially if you go from a desktop setup to a mobile setup multiple times per day.

Why is it a hardware issue?

Clock signals. HDMI has one and DisplayPort (what you're converting from) doesn't. So, when you plug in your HDMI monitor, there's no signal to sync up to. Rebooting usually resolves this and gets everything "synced up again." A passive adapter (what is in the hub) just rearranges the signal whereas an active adapter actually recreates the signal making it much more reliable.

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