iMac 27" 2020 crashes repeatedly when External Monitor is plugged in

The iMac runs perfectly when no external monitor is plugged, but as soon as the monitor is connected it crushes within an hour.

Did anyone found any solution to this problem?

It happened both with Catalina and after updating to BigSur

Thank you in advance to anyone responding.

Here is the error I get after restarting:

panic(cpu 2 caller 0xffffff800b36ea25): userspace watchdog timeout: no successful checkins from com.apple.WindowServer in 120 seconds

service: com.apple.logd, total successful checkins since load (763856 seconds ago): 76379, last successful checkin: 0 seconds ago

service: com.apple.WindowServer, total successful checkins since load (763826 seconds ago): 76363, last successful checkin: 120 seconds ago

service: com.apple.remoted, total successful checkins since load (763856 seconds ago): 76377, last successful checkin: 0 seconds ago



Backtrace (CPU 2), Frame : Return Address

0xffffffb0969db670 : 0xffffff80080b9aed 

0xffffffb0969db6c0 : 0xffffff80081fc6e3 

0xffffffb0969db700 : 0xffffff80081ecd1a 

0xffffffb0969db750 : 0xffffff800805ea2f 

0xffffffb0969db770 : 0xffffff80080b938d 

0xffffffb0969db890 : 0xffffff80080b9678 

0xffffffb0969db900 : 0xffffff80088be434 

0xffffffb0969db970 : 0xffffff800b36ea25 

0xffffffb0969db980 : 0xffffff800b36e678 

0xffffffb0969db9a0 : 0xffffff800884569e 

0xffffffb0969db9f0 : 0xffffff800b36dab4 

0xffffffb0969dbb20 : 0xffffff800884f86b 

0xffffffb0969dbc80 : 0xffffff80081a7d81 

0xffffffb0969dbd90 : 0xffffff80080bf0e7 

0xffffffb0969dbe00 : 0xffffff8008095905 

0xffffffb0969dbe60 : 0xffffff80080ad012 

0xffffffb0969dbef0 : 0xffffff80081d0ec3 

0xffffffb0969dbfa0 : 0xffffff800805f216 

      Kernel Extensions in backtrace:

         com.apple.driver.watchdog(1.0)[7AE04EA4-D026-39A0-B2D5-5C9E4EE72967]@0xffffff800b36d000->0xffffff800b36efff



Process name corresponding to current thread: watchdogd

Boot args: chunklist-security-epoch=0 -chunklist-no-rev2-dev



Mac OS version:

20C69



Kernel version:

Darwin Kernel Version 20.2.0: Wed Dec  2 20:39:59 PST 2020; root:xnu-7195.60.75~1/RELEASEX8664

Kernel UUID: 82E2050C-5936-3D24-AD3B-EC4EC5C09E11

KernelCache slide: 0x0000000007e00000

KernelCache base:  0xffffff8008000000

Kernel slide:      0x0000000007e10000

Kernel text base:  0xffffff8008010000

_HIB  text base: 0xffffff8007f00000

System model name: iMac20,1 (Mac-CFF7D910A743CAAF)

System shutdown begun: NO

Hibernation exit count: 0



System uptime in nanoseconds: 763861744423305

Last Sleep:           absolute           basetsc          base_nano

  Uptime  : 0x0002b6ba6bef13d4

  Sleep   : 0x0000000000000000 0x0000000000000000 0x0000000000000000

  Wake    : 0x0000000000000000 0x0000001b5478f86e 0x0000000000000000

last started kext at 754770714032314: >AudioAUUC 1.70 (addr 0xffffff7fa8583000, size 12288)

last stopped kext at 763795517110493: >usb.!UHostPacketFilter 1.0 (addr 0xffffff800ae5b000, size 8192)

loaded kexts:

org.virtualbox.kext.VBoxNetAdp 6.1.16

org.virtualbox.kext.VBoxNetFlt 6.1.16

org.virtualbox.kext.VBoxUSB 6.1.16

org.virtualbox.kext.VBoxDrv 6.1.16

AudioAUUC 1.70

@filesystems.smbfs 3.4.1

!ATopCaseHIDEventDriver 4020.6

!APlatformEnabler 2.7.0d0

AGPM 119

X86PlatformShim 1.0.0

@filesystems.autofs 3.0

@fileutil 20.036.15

!AHIDALSService 1

!AUpstreamUserClient 3.6.8

@kext.AMDRadeonX6000 4.0.2

@kext.AMDRadeonServiceManager 4.0.2

!AGraphicsDevicePolicy 6.2.2

@AGDCPluginDisplayMetrics 6.2.2

pmtelemetry 1

LuaHardwareAccess 1.0.16

|IOUserEthernet 1.0.1

!A!IKBLGraphics 16.0.1

|IO!BSerialManager 8.0.2f9

@DontStealMacOSX 7.0.0

!AHV 1

!ADiskImages2 1

!A!ICFLGraphicsFramebuffer 16.0.1

!AThunderboltIP 4.0.3

!ABridgeAudio!C 100.2

!A!ISlowAdaptiveClocking 4.0.0

!AMCCSControl 1.14

!A!IPCHPMC 2.0.1

!AGFXHDA 100.1.431

BridgeAudioCommunication 100.2

!AAVEBridge 6.1

!UCardReader 511.60.2

BCMWLANFirmware4378.Hashstore 1

BCMWLANFirmware4377.Hashstore 1

BCMWLANFirmware4364.Hashstore 1

BCMWLANFirmware4355.Hashstore 1

@filesystems.tmpfs 1

|!ABCM5701Ethernet 11.0.0

!ABCMWLANBusInterfacePCIeMac 1

@filesystems.hfs.kext 556.60.1

@BootCache 40

@!AFSCompression.!AFSCompressionTypeZlib 1.0.0

@!AFSCompression.!AFSCompressionTypeDataless 1.0.0d1

@filesystems.apfs 1677.60.23

@private.KextAudit 1.0

!AACPIButtons 6.1

!ASMBIOS 2.1

!AACPIEC 6.1

!AAPIC 1.7

@!ASystemPolicy 2.0.0

@nke.applicationfirewall 310

|IOKitRegistryCompatibility 1

|EndpointSecurity 1

!AHIDKeyboard 222

|IOUSBUserClient 900.4.2

!AMultitouchDriver 4400.28

!AInputDeviceSupport 4400.35

!AHS!BDriver 4020.6

IO!BHIDDriver 8.0.2f9

@kext.triggers 1.0

@kext.AMDRadeonX6200HWLibs 1.0

@kext.AMDRadeonX6000Framebuffer 4.0.2

@kext.AMDSupport 4.0.2

@kext.AMDRadeonX6000HWServices 4.0.2

|IOAVB!F 900.12

|IOAccelerator!F2 439.52

|IO!BHost!CUARTTransport 8.0.2f9

|IO!BHost!CTransport 8.0.2f9

X86PlatformPlugin 1.0.0

@!AGPUWrangler 6.2.2

|IOSlowAdaptiveClocking!F 1.0.0

!ASMBus!C 1.0.18d1

IOPlatformPlugin!F 6.0.0d8

|IONDRVSupport 585

|IOAudio!F 300.6.1

@vecLib.kext 1.2.0

!ASMBusPCI 1.0.14d1

!AGraphicsControl 6.2.2

@!AGraphicsDeviceControl 6.2.2

|IOGraphics!F 585

!A!ILpssUARTv1 3.0.60

!A!ILpssUARTCommon 3.0.60

!AOnboardSerial 1.0

@plugin.IOgPTPPlugin 900.11

|IOEthernetAVB!C 1.1.0

usb.cdc.ncm 5.0.0

usb.cdc 5.0.0

usb.networking 5.0.0

usb.!UHostCompositeDevice 1.2

!AHPM 3.4.4

!A!ILpssI2C!C 3.0.60

!A!ILpssI2C 3.0.60

!A!ILpssDmac 3.0.60

!AThunderboltPCIDownAdapter 4.1.1

!AThunderboltDPInAdapter 8.1.4

!AThunderboltDPAdapter!F 8.1.4

!AThunderboltNHI 7.2.8

|IOThunderbolt!F 9.3.2

!ABSDKextStarter 3

!ABCMWLANCoreMac 1.0.0

|IOSerial!F 11

|IO80211!FV2 1200.12.2b1

IOImageLoader 1.0.0

corecapture 1.0.4

|IOSurface 289.3

|IOSkywalk!F 1

mDNSOffloadUserClient 1.0.1b8

@filesystems.hfs.encodings.kext 1

usb.!UVHCIBCE 1.2

usb.!UVHCICommonBCE 1.0

usb.!UVHCI 1.2

usb.!UVHCICommon 1.0

!AEffaceableNOR 1.0

|IOUSB!F 900.4.2

|IOBufferCopy!C 1.1.0

|IOBufferCopyEngine!F 1

|IONVMe!F 2.1.0

usb.!UXHCIPCI 1.2

usb.!UXHCI 1.2

!AEFINVRAM 2.1

!AEFIRuntime 2.1

!ASMCRTC 1.0

|IOSMBus!F 1.1

|IOHID!F 2.0.0

$!AImage4 3.0.0

|IOTimeSync!F 900.11

|IONetworking!F 3.4

DiskImages 493.0.0

|IO!B!F 8.0.2f9

|IOReport!F 47

|IO!BPacketLogger 8.0.2f9

$quarantine 4

$sandbox 300.0

@kext.!AMatch 1.0.0d1

|CoreAnalytics!F 1

!ASSE 1.0

!AKeyStore 2

!UTDM 511.60.2

|IOUSBMass!SDriver 184.40.6

|IOSCSIBlockCommandsDevice 436.40.6

|IO!S!F 2.1

|IOSCSIArchitectureModel!F 436.40.6

!AMobileFileIntegrity 1.0.5

@kext.CoreTrust 1

!AFDEKeyStore 28.30

!AEffaceable!S 1.0

!ACredentialManager 1.0

KernelRelayHost 1

|IOUSBHost!F 1.2

!UHostMergeProperties 1.2

usb.!UCommon 1.0

!ABusPower!C 1.0

!ASEPManager 1.0.1

IOSlaveProcessor 1

!AACPIPlatform 6.1

!ASMC 3.1.9

|IOPCI!F 2.9

|IOACPI!F 1.4

watchdog 1

@kec.pthread 1

@kec.corecrypto 11.1

@kec.Libm 1