Display keeps waking up

I’m using the TBT3-UDZ with a 2019 MacBook Pro 16". I have an LG 27UD88-W connected to the hub via DisplayPort. The issue I’m seeing is when the MacBook goes to sleep or reboots, the monitor will show that it loses the signal, turn off and then turn back on again after about 2 seconds. It keeps repeating this cycle until I unplug the display port cable. The monitor beeps every time it turns back on.

I’m not sure if it’s the MacBook, the hub or the display but it’s driving me crazy. Do you have any tips for troubleshooting this?

I am running macOS 11.2.2.


Thank you for contacting Plugable support! Sorry to hear about this issue. I’d be more than happy to assist you.

  1. Can you say which DisplayPort this monitor is connected to, the “Display 1” or “Display 2” output?

  2. If you try switching to the other connection, do you still have the same behavior?

Please don’t hesitate to let us know of other questions.

Thanks again for contacting Plugable support and best wishes!

Joshua Henry

Senior Engineer | Product Owner
Plugable Technologies

I am currently using Display 2 but it occurs on both DisplayPorts. I just tried it again just now and I realized that it’s not as small of a loop as I originally thought. When I put the computer to sleep, it will turn off the monitor, turn it back on then off again once and then stay off for a bit. However if I leave the beep feature on the monitor (e.g. it beeps when it turns on) I can hear it beeping randomly from the other room so I know it keeps cycling long after I put the computer to sleep.

Fiddling around with this again this morning brought up a second issue. Let me know if I should create a separate topic for this but I can only get to 60Hz when using the Display 2 DP. I am aware of the opt-click trick on macOS to force the monitor to a given frequency but the “60 Hz” option is never available when I connect to Display 1; it’s greyed out and stuck on 30 Hz. The system information pane confirms that it is indeed at 30 Hz and the mouse movement lag is intolerable. When I connect it to Display 2, it sometimes takes a few cycles of plugging and unplugging the laptop and/or the display port cable from the hub before the 60 Hz option is available again. I haven’t figured out the exact ritual yet but I tried the same things on Display 1 and never succeeded at getting it to 60Hz on DP1.

HDMI seems to be ok but I find it has artifacts in the picture so I prefer DisplayPort. I ran with an HDMI cable for a week or so when I thought the DisplayPort wasn’t capable of 60Hz refresh at all and I don’t remember having seen this wake/sleep endless cycle issue. I do remember not being happy with the dithering around text. It was noticeably worst than when using DP. Maybe this is just monitor settings but I didn’t try debugging it.

Thanks for the information. I appreciate the details provided!

No need to create a new topic for the 30Hz issue. I think at this point we should try to get some additional information about the system and what’s happening with the dock and the attached display.

We have a troubleshooting tool that helps us find out what is going on in situations like this. Please plug the dock with your monitor attached to Display 1 (so I can check the 30Hz problem you’re seeing there) into your computer, then go to this page and follow the instructions there:


When emailing us the diagnostics results to support@plugable.com please reference ticket # 335779 in the subject line.

I can then look for any possible clues from a software perspective as to why you’re stuck at 30Hz

It may be possible that these issues are related to some macOS Big Sur display problems that were introduced with 11.1 and still appear to be problematic in the 11.3 beta: https://www.macrumors.com/2021/02/03/macos-big-sur-external-display-issues/

If we’re unable to find a solution we may ultimately need to offer you a return for a full refund if purchased from us via Amazon, Newegg, eBay, or Walmart. Or wait and see if the next macOS Big Sur update may help.


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Thanks for sending the diagnostics. Looking at them, I see your MacBook Pro 16" currently is detecting the dock as I would expect, and I can verify I also see the 30Hz issue. I also see your Mac appears to be on the latest macOS Big Sur 11.2.3 version.

Here’s what the system is reporting for your display, the resolution and refresh rate both look incorrect (reporting a “6K” display at 30Hz):

LG Ultra HD:

Resolution: 6016 x 3384

UI Looks like: 3008 x 1692 @ 30.00Hz
Framebuffer Depth: 30-Bit Color (ARGB2101010)
Main Display: Yes
Mirror: Off
Online: Yes
Rotation: Supported
Automatically Adjust Brightness: Yes
Connection Type: Thunderbolt/DisplayPort

This behavior may be related to some problems we’ve been seeing since macOS 11.1, where something changed in the OS that has caused incorrect resolutions and/or refresh rates for displays attached to Macs directly or through a dock like ours. You can see here it’s been a rather large issue affecting many users: https://www.macrumors.com/2021/02/03/macos-big-sur-external-display-issues/ We may be unable to resolve this behavior until a new version of Big Sur is released which addresses these problems users are experiencing. Unfortunately it appears the latest 11.3 beta is still affected.

For what we can do to try and resolve the issue, or at least improve behavior for now, I’ll make some recommendations below:

  1. Unplug the dock from the Mac
  2. Perform an SMC reset: https://support.apple.com/en-us/HT201295
  3. Perform an NVRAM/PRAM reset: https://support.apple.com/en-us/HT204063
  4. Plug the dock back in to the Mac and see if the behavior has improved

If that hasn’t helped, we can try to manually override the settings macOS is offering you:

  1. Choose Apple menu > System Preferences, then click Displays.
  2. Choose the display that you’d like to change the resolution for, then hold the Option key and select the Scaled button . Then the refresh rate drop down menu should appear.

Example (with the built in display):

To try address the other issue with this display not being able to stay in sleep mode correctly, I have heard of this behavior in a few other customer reports with this dock, but never before with this model display. This is the first report we’ve received with this monitor model being used with this dock.

Researching this monitor for possible clues to the sleep behavior I did not find anything that matched your description of the sleep problem, but others on Mac are seeing some other troubles too: https://discussions.apple.com/thread/8526209

Best wishes,


Hi Josh,

I have a similar issue with a MacBook Pro 16 2020 Big Sur 11.2 and using 2 screens. One is an LG on the DisplayPort it works exactly as it should no problems.

The other is an ASUS MX279 27” 1080p screen and this is the problem one. It’s connected from dock HDMI port with a HDMI-HDMI of which I have tried multiple cables. The problem presents any time my laptop sleeps and wakes up again. The screen turns on initially and will correctly show my screen at the expected resolution and then will just blink off and have no picture before blinking on back on again and just repeats this every few seconds. I can restore the screen to working by going into displays in system preferences and setting the screen to 50Hz and then back to 60Hz and it seems to work consistently until the next sleep of the laptop. I suspect just setting this value again corrects something and puts it back on the straight and narrow.

Before I got the dock a week or 2 ago I was using a USB-C-HDMI cable and didn’t experience the same issue so I’m not certain if it’s the Big Surr issues or something specific to the dock.

I have attempted both the SMC and NVRAM resets and continue to encounter the same problem.

Can you provide any suggestions?

Thanks Adam

Hi Adam (@Adament),

The issues you’ve described do match what other customers have reported after macOS 11.1 through 11.2.3 when used with devices like our TBT3-UDZ dock and others.

Big Sur 11.3 was just released, I’d recommend updating to 11.3 and see if these behaviors improve at all and we can go from there.

Thank you!

I just randomly tried to connect my monitor to the other DisplayPort today (I’ve been on 11.3 for a little while now) and it automatically detected at 60Hz so this seems to be resolved at least for me.

However I am still seeing the display turn on/off when my MacBook Pro goes to sleep. I also have a whole new issue where my laptop kernel panics about 1/5 times when I connect to the dock. I’m going to upgrade to 11.4 soon but I don’t have my hopes up.

No such luck, it seemed a bit more reliable for the day or 2 after updating but since it still goes into that on and off cycle I was seeing before. On the plus side I’ve got a keyboard shortcut that does the refresh change 60Hz -> 50Hz -> 60Hz that makes it go back to working correctly. Until it sleeps or something else that does a full screen change.

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Thanks for the tip. I have exactly the same problem and I was getting sick of having to shutdown unplug and restart my macbook. Its good to know it is not just my mac having the problem.I really hope the problem is fixed soon or I will need to look at returning the product as not fit for purpose.

@ Joshua_H - Does plugable release firmware upgrades to fix problems like these or should I look elsewhere? Thanks.

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