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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          basenano   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 @DontStealMacOS_X 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