macOS stutters every 2 seconds when an external monitor is plugged in

[DiPech]

I’ve bought a new Macbook Pro 16”. There is stuttering right after I have my external monitor plugged in. Stuttering is observed on both displays (on the internal Retina and on the external LG display) while having connected the external LG display. Stuttering stops immediately right after ejecting the LG display.

There are two videos I’ve recorded to show this problem (3 stutters during two 6-seconds videos):
YouTube – Stuttering when moving a window.
YouTube – Stuttering when selecting a text.

My specs:

• Notebook: Macbook Pro 16” 2019, 8-Core Intel Core i9, 16 GB RAM, 1TB SSD, Intel UHD Graphics 630, AMD Radeon Pro 5500M (4GB).
• External Monitor: LG 29UM69G 29”.
• OS Version: Catalina, 10.15.5 (19F101).
• Periphery: Magic Keyboard 2, Magic Mouse 2, USB 2.0 no-name Mouse, original Apple USB-C to USB-C 0.8M cable (Apple Thunderbolt 3), HDMI to HDMI cable through original 3-in-1 adapter USB-C to [ USB-C, HDMI, USB 2.0 ].

What doesn’t help at all:

• Installing the last update.
• Connecting through USB-C-to-USB-C Thunderbolt 3 cable (instead of HDMI-to-HDMI plus HDMI-to-USB-C connector) – I’ve bought it just for solving this issue.
• Resetting SMC and NVRAM.
• Using another (new) user profile.
• Closing the lid and working only with the external display.
• Having both displays working but showing separate desktops.
• Having both displays working with turned on displays mirroring.
• Setting custom scaling (also tried choosing custom scaling by pressing Option key).
• Using the built-in trackpad.
• Turning off Bluetooth.
• Using no-name USB2.0 wired mouse.
• Removing mouse and trackpad plists from Libraries/Preferences folder.
• The Diagnostic Tool (by pressing D) shows “No Issues Found”.
• The Disk Utility Tool (by pressing Cmd + R) shows “No Issues Found”.

What helps (but these are not solutions):

• Eject external display.
• Using Bootcamp (this problem is not observed there at all).
• Booting in Safe Mode (by pressing Shift after starting a computer).
• Using my previous MacBook Pro 2015 15” (which also works under the last Catalina version) with the LG display.

Please, don’t offer these possible solutions, they aren’t acceptable for me:

• Return the MacBook to the store.
• Reinstall macOS from scratch.

P.S. AppleCare support doesn't help me

Please, can anybody help with it?

 

[Raz0rEdge]

Start up Activity Monitor and go the CPU tab and sort by highest CPU usage. With the external display unplugged, do the actions that usually cause stuttering and take note of anything that spikes. Plug the external display and re-do the things that cause the stuttering and see if you see any spikes. Take note of what is spiking (if anything) and that should be investigated next.

If possible, try connecting to the display without any adapters or hubs to eliminate that as an issue.

At work, I have a Wavelink USB-C hub hat supports 2 external monitors. That thing uses the USB interface to transfer the video and then sends it to the displays over HDMI and I've noticed that sometimes if there's a LOT of activity on one of the external monitors, the MBP can start to slow/stutter for other actions.

 

[Slydude]

My first guess is to check the cables/adapters being used. That can cause the kind of bickering that you have noticed.

The second thing to check has to be done with the second monitor in place and it will help to have the monitor's manual handy. Check the list of supported resolutions and see if the resolution you want to use is supported at the timing frequency being used. My LG monitor, for example, supports timing frequencies of 50, 60 or 70 Hertz and 60 Hz seems to be the default. This kind of issue is usually taken care of by the OS with little/no user intervention but you never know.

Since the monitor works under BootCamp I'd boot there first and check the resolution and timing frequency settings. Then reboot to macOS and duplicate those settings to see if that solves the problems.

×

 

[DiPech]

Raz0rEdge, Slydude, thanks to you for the answers!

Take note of what is spiking (if anything) and that should be investigated next.

I did it. There is nothing special.

try connecting to the display without any adapters or hubs to eliminate that as an issue.

My first guess is to check the cables/adapters being used.

I've tried two approaches: USBc-USBc Thunderbolt 3 original cable and HDMI-HDMI-through-HDMI-USBc-converter cable. There is no different behavior between them.

Since the monitor works under BootCamp I'd boot there first and check the resolution and timing frequency settings. Then reboot to macOS and duplicate those settings to see if that solves the problems.

I've checked it. LG monitor has the same settings (resolution, frequency) under Bootcamp as well as under macOS. Nevertheless, I've tried to play with settings (resolution, frequency, scaling, mirroring) – nothing had helped.

 

[DiPech]

UPD: I did a completely fresh installation. The problem is still here...

 

[ferrarr]

When you try the NVRAM and SMC resets, try them multiple times separately.

 

[DiPech]

I've already tried it. Three times in a row each.