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Random UI freezes

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Hello there,


since upgrading to Catalina (and now also Big Sur) I have random UI freezes. It starts with the active program (any program is affected at some time...) becoming unresponsive, mission control and switching to other programs still works and then step by step the whole system gets affected and I'll have to watch the beachball, sometimes for a few seconds, up to around 1 minute. Then all the stuff I did in that time gets executed at ones. Typing, opening new taps (even typing web adresses), Mission Control, opening programs from the dock and so on.

The freezes happen totally random. No abnormalities in the activity monitor (I looked at cpu, memory, gpu in several different freezes). 

Before upgrading to Catalina my system was running fine with Mojave.

I did an opencore installation and followed exactly the guide from dortania for IvyBridge CPUs, everything else is working perfect. Since switching to iMacPro1,1 even wake up from sleep doesn't give me a blackscreen.

I tried different smbios (iMac12,1 - iMac15,1 - iMacPro1,1 and a Mac Pro, don't remember the exact model).


I have the following build:


CPU: Intel i5 3470

GPU: Sapphire RX580 Nitro+ 4GB

Mainboard: ASRock H77 Pro4M

RAM: 4x4 GB G.Skill Sniper


CSM disabled


I discovered that I have some graphic glitches when booting, no matter if it's linux, macOS or windows. Shortly after every (!) startup or reaching the login screen a random line flashes somewhere from left to right across my screen for a fraction of a second, but no glitches after that at all. No problems in windows while gaming or stress testing my gpu.


I am very thankful for any help provided since this is a big problem in everyday work, pushing my blood pressure up the limits... 

Thank you very much



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  • 1 month later...

Reset Your NVRAM -

  1. Press and hold the power button on your Mac to completely shut it off

  2. Power on your Mac.

  3. Immediately after you hear the startup sound, press and hold the Command + Option + P + R keys.

  4. Keep holding them down until you hear the startup sound again.

  5. Release the keys, and the NVRAM will have reset.

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