MBP 16" choppy mouse and window movement on external 4K display

[plind]

I connected my new MBP 16" with 8GB AMD Radeon 5500M to my LG 32UD89-W 4k monitor through the USB-C and unfortunately movements in general are very jerky. You notice it most with mouse movements, but when you drag a window around, you see the same choppiness. On the internal display movements are far smoother (also with the external monitor connected).

I recorded the movements in slow motion:

1. Here's the one on the internal display:
2. Hre's the one on the external display:

Notice the huge jumps on the external display.

I'm hoping this is an AMD driver issue that will be resolved soon. Does anyone have a similar experience?

 

[Alaska99801]

Are you running at 30hz on the external monitor? It appears thats your problem.

 

[plind]

I wanted to deny this, since I would assume -using the DisplayPort over USB-C connection- this would always be @60Hz by default. But in trying to find the current refresh rate in my display settings, I switched the scaling a bit and things now do seem smoother. After this I checked my display settings in the Systems Report and that does read 60Hz. So I guess it might indeed have been at 30Hz when recording the video. I'll double check the System Report should I experience the choppiness again. Thanks for your reply!