Hi glezbsg. Good one - you may have spotted something here.
FYI, you can see the logs (System log in this case) here:
Control panel all items/Administrative Tools/Event Viewer/Windows logs/System
When you say you have seen the Defender message dozens of times - I assume you mean, separated, once every reboot, not dozens in succession? And in that sense, Yes.. So KB 2267602 (Defender) is successfully installed - then freezes the system! But it then gets more interesting - clearly this is the precursor to the dots freeze. See the sequence below, with a pause in time before the hard restart shown.
(NB, the time sequence here is bottom up, as per the log. "=" between each message at this point.)
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Then off & away on the reboot processes
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23:11:31 The process C:\Windows\System32\RuntimeBroker.exe (AJAS8) has initiated the restart of computer AJAS8 on behalf of user AJAS8\andy for the following reason: Other (Unplanned)
Reason Code: 0x0
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23:10:35 The start type of the Windows Modules Installer service was changed from demand start to auto start.
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23:08:28 The application-specific permission settings do not grant Local Activation permission for the COM Server application with CLSID
{2593F8B9-4EAF-457C-B68A-50F6B8EA6B54}
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22:49:49 Installation Successful: Windows successfully installed the following update: Security Intelligence Update for Microsoft Defender Antivirus - KB2267602 (Version 1.373.1190.0) Reason Code: 0x0
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Prior to this, long sequence of messages in rapid succession, as normal, but ending with 6 seconds to install KB2267602
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SO - does that mean that Defender does not like 5016616 etc?
Next - so can Defender be made inactive? No time now - 02:25 here in UK
Final note to check more: KB2267602 is showing installed on my PC - but on the day (4/9) when 5016616 was no longer offered - and replacement KB5017308 not yet born. So I got through an Update cycle without freeze. VERY interesting. But I have not tried again since - have to actually use the PC sometimes.