Catalina se estrella en el cierre: "watchdog timeout: no checkins from watchdogd"

Tengo un iMac de finales de 2012 con 24GB o RAM y 3 discos USB conectados a él, todos corriendo time machine en secuencia.

Después de actualizar a catalina, cada vez que apago el sistema tarda mucho en apagarse y después de alcanzar el estado de apagado, a veces la pantalla se vuelve blanca de nuevo, como si fuera a arrancar de nuevo y después de un rato la pantalla se vuelve negra de nuevo con un mensaje de apagado en el medio, en varios idiomas.

Entonces, si inicio el sistema, veo este mensaje de bloqueo:

panic(cpu 1 caller 0xffffff7fa6c96aae): watchdog timeout: no checkins from watchdogd in 184 seconds (97 totalcheckins since monitoring last enabled), shutdown in progress
Backtrace (CPU 1), Frame : Return Address
0xffffff82e0b13c40 : 0xffffff802553f98b 
0xffffff82e0b13c90 : 0xffffff8025676c15 
0xffffff82e0b13cd0 : 0xffffff802566861e 
0xffffff82e0b13d20 : 0xffffff80254e6a40 
0xffffff82e0b13d40 : 0xffffff802553f077 
0xffffff82e0b13e40 : 0xffffff802553f45b 
0xffffff82e0b13e90 : 0xffffff8025cd2e05 
0xffffff82e0b13f00 : 0xffffff7fa6c96aae 
0xffffff82e0b13f10 : 0xffffff7fa6c96472 
0xffffff82e0b13f50 : 0xffffff7fa6cabfd6 
0xffffff82e0b13fa0 : 0xffffff80254e613e 
      Kernel Extensions in backtrace:
         com.apple.driver.watchdog(1.0)[58392D62-D9E8-3022-85C1-B78AC93B9167]@0xffffff7fa6c95000->0xffffff7fa6c9dfff
         com.apple.driver.AppleSMC(3.1.9)[EB9D605D-85B1-3506-8B2E-ABD195817A4F]@0xffffff7fa6c9e000->0xffffff7fa6cbcfff
            dependency: com.apple.iokit.IOACPIFamily(1.4)[9BA2613C-A129-3EDD-8DC1-2CFF6B62B832]@0xffffff7fa6c8c000
            dependency: com.apple.driver.watchdog(1)[58392D62-D9E8-3022-85C1-B78AC93B9167]@0xffffff7fa6c95000
            dependency: com.apple.iokit.IOPCIFamily(2.9)[E6E855AD-A5B2-3518-A997-1384B4360708]@0xffffff7fa5f2f000

BSD process name corresponding to current thread: kernel_task

Mac OS version:
19A583

Kernel version:
Darwin Kernel Version 19.0.0: Wed Sep 25 20:18:50 PDT 2019; root:xnu-6153.11.26~2/RELEASE_X86_64
Kernel UUID: 70EDD61F-8D909B78160
Kernel slide:     0x0000000025200000
Kernel text base: 0xffffff8025400000
__HIB  text base: 0xffffff8025300000
System model name: iMac13,2 (Mac-FC02E91DDD3FA6A4)
System shutdown begun: YES
Panic diags file available: NO (0xe00002cd)

System uptime in nanoseconds: 1201012930700
last loaded kext at 692174279981: @filesystems.msdosfs  1.10 (addr 0xffffff7fa9e1c000, size 69632)
last unloaded kext at 67316368087: >!AXsanScheme    3 (addr 0xffffff7fa89a7000, size 40960)
loaded kexts:
com.Cycling74.driver.Soundflower    2
@filesystems.msdosfs    1.10
>!A!BMultitouch 97
>AudioAUUC  1.70
>!AGraphicsDevicePolicy 4.1.46
@AGDCPluginDisplayMetrics   4.1.46
>!AHV   1
|IOUserEthernet 1.0.1
|IO!BSerialManager  7.0.0f8
>AGPM   111.1.18
>!APlatformEnabler  2.7.0d0
>X86PlatformShim    1.0.0
>pmtelemetry    1
>!AUpstreamUserClient   3.6.8
>!AHDAHardwareConfigDriver  283.14
>!AMikeyHIDDriver   131
@Dont_Steal_Mac_OS_X    7.0.0
@GeForce    14.0.0
>!A!IHD4000Graphics 14.0.0
>AGDCBacklightControl   4.1.46
>!AHDA  283.14
>eficheck   1
>!AMikeyDriver  283.14
>ACPI_SMC_PlatformPlugin    1.0.0
>!AThunderboltIP    3.1.3
>!ABacklight    170.18
>!ALPC  3.1
>!ASMCLMU   212
>!AFIVRDriver   4.1.0
>!A!ISlowAdaptiveClocking   4.0.0
>!A!IFramebufferCapri   14.0.0
@nvidia.NVDAStartup 14.0.0
>!AMCCSControl  1.12
@fileutil   20.036.15
@filesystems.autofs 3.0
>!AVirtIO   1.0
@filesystems.hfs.kext   522.0.9
@!AFSCompression.!AFSCompressionTypeDataless    1.0.0d1
@BootCache  40
@!AFSCompression.!AFSCompressionTypeZlib    1.0.0
@filesystems.apfs   1412.11.7
|!ABCM5701Ethernet  10.3.5
@private.KextAudit  1.0
>!ASDXC 1.7.7
>AirPort.Brcm4360   1400.1.1
>!AAHCIPort 341.0.2
>!AACPIButtons  6.1
>!ARTC  2.0
>!AHPET 1.8
>!ASMBIOS   2.1
>!AACPIEC   6.1
>!AAPIC 1.7
>!A!ICPUPowerManagementClient   222.0.0
$!AImage4   1
@nke.applicationfirewall    302
$TMSafetyNet    8
@!ASystemPolicy 2.0.0
>!A!ICPUPowerManagement 222.0.0
|EndpointSecurity   1
>usb.cdc.acm    5.0.0
>usb.serial 6.0.0
>usb.cdc.ecm    5.0.0
>usb.cdc.ncm    5.0.0
>usb.cdc    5.0.0
>!UMergeNub 900.4.2
>!AXsanScheme   3
>!A!BHIDKeyboard    209
>!AHIDKeyboard  209
>IO!BHIDDriver  7.0.0f8
>!AMultitouchDriver 3400.35
>!AInputDeviceSupport   3400.27
>!AGraphicsControl  4.1.46
|IOAVB!F    800.17
>!ASSE  1.0
@nvidia.driver.NVDAGK100Hal 14.0.0
@nvidia.driver.NVDAResman   14.0.0
>DspFuncLib 283.14
@kext.OSvKernDSPLib 529
>IOPlatformPluginLegacy 1.0.0
@!AGPUWrangler  4.1.46
>!ABacklightExpert  1.1.0
|IONDRVSupport  558.3
>!AHDA!C    283.14
|IOHDA!F    283.14
|IOAudio!F  300.2
>!ASMBusPCI 1.0.14d1
>X86PlatformPlugin  1.0.0
>IOPlatformPlugin!F 6.0.0d8
|IOSlowAdaptiveClocking!F   1.0.0
|IOAccelerator!F2   438.1.23
@!AGraphicsDeviceControl    4.1.46
>!AThunderboltEDMSink   4.2.0
>!ASMBus!C  1.0.18d1
|IOGraphics!F   558.3
@plugin.IOgPTPPlugin    800.14
@kext.triggers  1.0
>Core!S 551
|Broadcom!BHost!CUSBTransport   7.0.0f8
|IO!BHost!CUSBTransport 7.0.0f8
|IO!BHost!CTransport    7.0.0f8
|IO!B!F 7.0.0f8
|IO!BPacketLogger   7.0.0f8
>usb.IOUSBHostHIDDevice 1.2
@vecLib.kext    1.2.0
>usb.networking 5.0.0
>usb.!UHostCompositeDevice  1.2
>usb.!UHub  1.2
|IOSerial!F 11
@filesystems.hfs.encodings.kext 1
|IOSurface  269.6
>!AThunderboltDPOutAdapter  6.2.3
>!AThunderboltDPInAdapter   6.2.3
>!AThunderboltDPAdapter!F   6.2.3
>!AThunderboltPCIDownAdapter    2.5.2
>!AThunderboltNHI   5.5.8
|IOThunderbolt!F    7.4.5
|IOEthernetAVB!C    1.1.0
|IOAHCIBlock!S  316.0.5
|IO80211!F  1200.12.2b1
|IOSkywalk!F    1
>mDNSOffloadUserClient  1.0.1b8
>corecapture    1.0.4
|IOAHCI!F   290.0.1
>usb.!UEHCIPCI  1.2
>usb.!UEHCI 1.2
>usb.!UXHCIPCI  1.2
>usb.!UXHCI 1.2
>usb.!UHostPacketFilter 1.0
|IOUSB!F    900.4.2
>!AEFINVRAM 2.1
>!AEFIRuntime   2.1
|IOSMBus!F  1.1
|IOHID!F    2.0.0
$quarantine 4
$sandbox    300.0
@kext.!AMatch   1.0.0d1
>DiskImages 493.0.0
>!AFDEKeyStore  28.30
>!AEffaceable!S 1.0
>!AKeyStore 2
>!UTDM  489.11.2
|IOSCSIBlockCommandsDevice  422.0.2
>!ACredentialManager    1.0
>KernelRelayHost    1
>!ASEPManager   1.0.1
>IOSlaveProcessor   1
|IOUSBMass!SDriver  157.11.2
|IOSCSIArchitectureModel!F  422.0.2
|IO!S!F 2.1
|IOUSBHost!F    1.2
>!UHostMergeProperties  1.2
>usb.!UCommon   1.0
>!ABusPower!C   1.0
|CoreAnalytics!F    1
>!AMobileFileIntegrity  1.0.5
@kext.CoreTrust 1
|IOTimeSync!F   800.14
|IONetworking!F 3.4
|IOReport!F 47
>!AACPIPlatform 6.1
>!ASMC  3.1.9
>watchdog   1
|IOPCI!F    2.9
|IOACPI!F   1.4
@kec.pthread    1
@kec.corecrypto 1.0
@kec.Libm   1

Me llama la atención esta línea @filesystems.msdosfs ... SISTEMA DE ARCHIVOS MS DOS???? ¡WTF!

Mis ideas eran reiniciar el SMC e intentar un arranque seguro. Ninguna de las dos cosas solucionó el problema, que persiste.

¿Qué pasos siguientes podrían ayudarme a evitar el choque?