Crash when left idle (using Vega 64 on x299)

Hey guys,

I am stumped by a problem where my Hackintosh would crash if left idle. Everything else works fine.

1. Sleep
2. Sound
3. USB
4. Bluetooth

Here are the details of the system:

1. Asrock Taichi x299 with 9800x processor
2. 64GB RAM
3. Using latest Clover 5113
4. Using boot flags: npci=0x2000 darkwake=0
5. Using latest version of kexts:
   FakeSMC
   AppleALC
   IntelMausiEthernet
   Lilu
   TSCAdjustReset
   WhateverGreen
6. Drivers
   ApfsDriverLoader
   AptioMemoryFix
   AudioDxe
   DataHubDxe
   FSInject
   HFSPlus
   NvmExpressDxe
   SMCHelper

I have tried the following but doesn't help

1. adding shikigva=18
2. adding shikigva=60 - system doesn't even complete boot
3. swapID.kext
4. AGPMEnabler.kext
5. Opencore - doesn't work with my system as Patch APIC is required for my CPU (otherwise validate topology fails with 16 processors vs 17 processors)
6. Moved graphics cards from PCI slot 1 to PCI slot 3
7. Cleared NVRAM

I see DumpGPURestart in logs when the crash happens. The funny thing is that the computer could be idle after the boot if I don't login.