Microsoft Defender had no engine or signatures loaded until MpCmdRun.exe -WdEnable was run

I encountered an unusual Microsoft Defender state on Windows where Defender appeared to be installed, but its protection engine and signatures were not actually loaded.

Initial diagnostics showed:

• WinDefend would not remain running.
• Get-MpComputerStatus reported AMRunningMode as "Not running".
• AMServiceEnabled, AntivirusEnabled, AntispywareEnabled, and RealTimeProtectionEnabled were False.
• AMEngineVersion was 0.0.0.0.
• AntivirusSignatureVersion and AntispywareSignatureVersion were empty.
• Get-MpPreference failed with HRESULT 0x800106ba.
• MpCmdRun.exe -ResetPlatform also failed with 0x800106ba.
• SecurityCenter2 AntiVirusProduct, AntiSpywareProduct, and FirewallProduct classes returned zero instances.
• WSCGetSecurityProviderHealth returned Health = 2.

The PC had previously used Avast, but Avast had already been removed before this investigation. The problem persisted after its removal.

I also ran DISM successfully and SFC repaired some corrupt files, but Microsoft Defender remained non-functional.

Further investigation showed that WdFilter.sys existed and appeared valid, but the WdFilter minifilter was absent from the output of:

fltmc filters

The issue was finally resolved by locating the current Microsoft Defender Platform directory and running:

MpCmdRun.exe -WdEnable

Immediately after running this command:

• WinDefend started successfully.
• WdFilter appeared in fltmc filters.
• AMRunningMode changed to Normal.
• AMServiceEnabled became True.
• AntivirusEnabled became True.
• AntispywareEnabled became True.
• RealTimeProtectionEnabled became True.
• The Defender engine and security intelligence versions loaded normally.

Microsoft Defender has remained operational since then.

My question is: what could cause Microsoft Defender to enter this state where the engine, signatures, service, and WdFilter minifilter were effectively inactive, yet running MpCmdRun.exe -WdEnable immediately restored the entire Defender stack?

Could this indicate that Defender had been left in a disabled platform state by a previous third-party antivirus installation or removal?

I documented the same incident in Feedback Hub, including diagnostics and a screenshot:

Feedback Hub report: https://aka.ms/AA11uk3h

The issue is already resolved. I am mainly trying to understand the likely root cause and whether this behavior indicates a Defender platform state or registration issue that Microsoft should investigate.