8700k + RX 580 UI lag?

Hi,

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i've got my vanilla install working but sometimes when i switch between desktops or i use the mission control i can clearly see the UI lagging (i guess that it goes lower than 20 fps).

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What i've tried so far:

- Using different SMBIOSes: 17.1, 18.1, 18.2, and 18.3

- Using different ig-platform-id: 0x3E9B0007 and 0x3E920003 (for each SMBIOS above)

- Using different another DisplayPort

- Recompiled and installed WhateverGreen and Lilu with the latest GitHub changes

- Removing all USB devices

- Update the BIOS to the latest version

- Flip the GPU BIOS switch

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I've a dual-monitor setup: 4k scaled to 1080 + a native 1080 monitor.

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https://i.redd.it/ywp519ro8l421.png

Motherboard: ROG STRIX Z370-I GAMING

GPU: SAPPHIRE NITRO+ RADEON RX 580 8GB

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The fun fact is that my system used to be buttery smooth for more than a year with High Sierra. The issue presented with Mojave.

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Any idea?