This sounds exactly like my scenario, except on a iMac Retina 5k 4-core i7. Literally *nothing* else open on the system except the time machine backup was in progress. panic(cpu 4 caller 0xffffff801af53a13): userspace watchdog timeout: no successful checkins from com.apple.WindowServer in 120 seconds service: com.apple.logd, total successful checkins since wake (2450 seconds ago): 246, last successful checkin: 0 seconds ago service: com.apple.WindowServer, total successful checkins since wake (2450 seconds ago): 226, last successful checkin: 120 seconds ago Backtrace (CPU 4), Frame : Return Address 0xffffffc122aa3670 : 0xffffff8017cbc66d 0xffffffc122aa36c0 : 0xffffff8017dff073 0xffffffc122aa3700 : 0xffffff8017def6aa 0xffffffc122aa3750 : 0xffffff8017c61a2f 0xffffffc122aa3770 : 0xffffff8017cbbf0d 0xffffffc122aa3890 : 0xffffff8017cbc1f8 0xffffffc122aa3900 : 0xffffff80184bee84 0xffffffc122aa3970 : 0xffffff801af53a13 0xffffffc122aa3980 : 0xffffff801af536ba 0xffffffc122aa39a0 : 0xffffff80184460ee 0xffffffc122aa39f0 : 0xffffff801af52b0a 0xffffffc122aa3b20 : 0xffffff80184502bb 0xffffffc122aa3c80 : 0xffffff8017daaa61 0xffffffc122aa3d90 : 0xffffff8017cc1d77 0xffffffc122aa3e00 : 0xffffff8017c985d5 0xffffffc122aa3e60 : 0xffffff8017cafb82 0xffffffc122aa3ef0 : 0xffffff8017dd3823 0xffffffc122aa3fa0 : 0xffffff8017c62216 Kernel Extensions in backtrace: com.apple.driver.watchdog(1.0)[7948A279-A8B8-3650-AFBF-B1E3EB68942A]@0xffffff801af52000->0xffffff801af53fff Process name corresponding to current thread: watchdogd Mac OS version: 20B29 Kernel version: Darwin Kernel Version 20.1.0: Sat Oct 31 00:07:11 PDT 2020; root:xnu-7195.50.7~2/RELEASEX8664 Kernel UUID: 84C6DC45-6B02-335F-9439-5D2A9BC385A4 KernelCache slide: 0x0000000017a00000 KernelCache base: 0xffffff8017c00000 Kernel slide: 0x0000000017a10000 Kernel text base: 0xffffff8017c10000 _HIB text base: 0xffffff8017b00000 System model name: iMac17,1 (Mac-DB15BD556843C820) System shutdown begun: NO Panic diags file available: YES (0x0) Hibernation exit count: 0 System uptime in nanoseconds: 3358413001062 Last Sleep: absolute basetsc basenano Uptime : 0x0000030df10394b8 Sleep : 0x000000d04ffdecad 0x000000008a916b60 0x000000c1ec725d0c Wake : 0x000000d0578da6d1 0x000000008b097b9a 0x000000d05679b0f8 last started kext at 3243326094155: >usb.!UUserHCI 1 (addr 0xffffff7fb77ef000, size 98304) last stopped kext at 3304242613422: >usb.!UUserHCI 1 (addr 0xffffff7fb77ef000, size 98304) loaded kexts: @filesystems.smbfs 3.4.1 @fileutil 20.036.15 @filesystems.autofs 3.0 AudioAUUC 1.70X86PlatformShim 1.0.0AGPM 119!APlatformEnabler 2.7.0d0!AUpstreamUserClient 3.6.8 @kext.AMDFramebuffer 4.0.0!AMikeyHIDDriver 131 @kext.AMDRadeonX4000 4.0.0!AMikeyDriver 283.15 @kext.AMDRadeonServiceManager 4.0.0!AHDA 283.15!A!ISKLGraphics 16.0.0!AGraphicsDevicePolicy 6.1.27!A!IPCHPMC 2.0.1 @AGDCPluginDisplayMetrics 6.1.27!A!ISKLGraphicsFramebuffer 16.0.0pmtelemetry 1LuaHardwareAccess 1.0.16 |IOUserEthernet 1.0.1 |IO!BSerialManager 8.0.1f5 @DontStealMacOS_X 7.0.0!AHV 1!ADiskImages2 1 @kext.AMD7000!C 4.0.0eficheck 1!ASMCLMU 212 |Broadcom!B20703USBTransport 8.0.1f5!AThunderboltIP 4.0.3!AMCCSControl 1.14!A!ISlowAdaptiveClocking 4.0.0!ATopCaseHIDEventDriver 4000.27!UTopCaseDriver 4000.27 @filesystems.tmpfs 1 @filesystems.hfs.kext 556.41.1 @BootCache 40 @!AFSCompression.!AFSCompressionTypeZlib 1.0.0 @!AFSCompression.!AFSCompressionTypeDataless 1.0.0d1 @filesystems.apfs 1677.50.1!ASDXC 1.9.0 |!ABCM5701Ethernet 11.0.0AirPort.BrcmNIC 1400.1.1!AAHCIPort 346 @private.KextAudit 1.0!AACPIButtons 6.1!ARTC 2.0!ASMBIOS 2.1!AACPIEC 6.1!AAPIC 1.7 @!ASystemPolicy 2.0.0 @nke.applicationfirewall 310 |IOKitRegistryCompatibility 1 |EndpointSecurity 1 @kext.triggers 1.0 @kext.AMDRadeonX4030HWLibs 1.0 @kext.AMDRadeonX4000HWServices 4.0.0DspFuncLib 283.15 @kext.OSvKernDSPLib 529!AGraphicsControl 6.1.27!ASMBusPCI 1.0.14d1 |IOAccelerator!F2 439.35.4 |IOSerial!F 11 |IOAVB!F 900.12 @plugin.IOgPTPPlugin 900.11 |IOEthernetAVB!C 1.1.0!AHDA!C 283.15 |IOHDA!F 283.15 |IOAudio!F 300.6.1 @vecLib.kext 1.2.0 @kext.AMDSupport 4.0.0 |Broadcom!BHost!CUSBTransport 8.0.1f5 |IO!BHost!CUSBTransport 8.0.1f5 |IO!BHost!CTransport 8.0.1f5 @!AGPUWrangler 6.1.27 @!AGraphicsDeviceControl 6.1.27!AThunderboltEDMSink 5.0.3 |IONDRVSupport 585 |IOGraphics!F 585!ASMBus!C 1.0.18d1X86PlatformPlugin 1.0.0IOPlatformPlugin!F 6.0.0d8 |IOSlowAdaptiveClocking!F 1.0.0!AHS!BDriver 4000.27IO!BHIDDriver 8.0.1f5!AMultitouchDriver 4400.28!AInputDeviceSupport 4400.35!AHIDKeyboard 222usb.IOUSBHostHIDDevice 1.2usb.networking 5.0.0usb.!UHostCompositeDevice 1.2!AThunderboltDPOutAdapter 8.1.4!AThunderboltDPInAdapter 8.1.4!AThunderboltDPAdapter!F 8.1.4!AThunderboltPCIDownAdapter 4.1.1!ABSDKextStarter 3 |IOSurface 289.3 @filesystems.hfs.encodings.kext 1 |IOAHCIBlock!S 332!AThunderboltNHI 7.2.8 |IOThunderbolt!F 9.3.2 |IONVMe!F 2.1.0 |IO80211!F 1200.12.2b1 |IOSkywalk!F 1mDNSOffloadUserClient 1.0.1b8corecapture 1.0.4 |IOUSB!F 900.4.2 |IOAHCI!F 294usb.!UXHCIPCI 1.2usb.!UXHCI 1.2!AEFINVRAM 2.1!AEFIRuntime 2.1 |IOSMBus!F 1.1 |IOHID!F 2.0.0 $!AImage4 3.0.0 |IOTimeSync!F 900.11 |IONetworking!F 3.4DiskImages 493.0.0 |IO!B!F 8.0.1f5 |IOReport!F 47 |IO!BPacketLogger 8.0.1f5 $quarantine 4 $sandbox 300.0 @kext.!AMatch 1.0.0d1 |CoreAnalytics!F 1!ASSE 1.0!AKeyStore 2!UTDM 511.40.9 |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 1.0KernelRelayHost 1 |IOUSBHost!F 1.2!UHostMergeProperties 1.2usb.!UCommon 1.0!ABusPower!C 1.0!ASEPManager 1.0.1IOSlaveProcessor 1!AACPIPlatform 6.1!ASMC 3.1.9 |IOPCI!F 2.9 |IOACPI!F 1.4watchdog 1 @kec.pthread 1 @kec.corecrypto 1.0 @kec.Libm 1