Quick fix: Stop and delete leftover download state. Close Update Assistant. Open Task Manager → End any Windows10Upgrade / setupprep processes. Delete folders: C:\$Windows.~BT, C:\Windows10Upgrade, and %LocalAppData%\Microsoft\Windows10Upgrade. Download fresh Update Assistant from microsoft.com/software-download/windows11. Run as Admin. Ensure 25GB+ free disk space. Connect to a stable Wi-Fi or wired network.

Update Assistant downloads files, fails (network drop, disk issue, AV interference), restarts from zero. Cause: incomplete download state corruption, network instability, or antivirus blocking. Reset everything to start fresh.

Symptom: Windows 11 Update Assistant restarts download from zero repeatedly.
Affects: Windows 11 Update Assistant.
Fix time: ~30 minutes (plus download).

What causes this

Update Assistant resumes partial downloads only if state is consistent. Issues:

Network drops during download — cached state inconsistent.
Antivirus scans / quarantines update files.
Disk space ran out, then freed — cache state corrupt.
Previous install crashed, leftover state confuses retries.
Specific KB has missing prerequisites.

Method 1: Clean up state and start fresh

The standard route.

Close any running Update Assistant.
Open Task Manager. End tasks:
- Windows10UpgraderApp.exe
- setupprep.exe
- SetupHost.exe
- Windows11InstallationAssistant.exe
Show hidden files in File Explorer (View → Show → Hidden items).
Delete these folders (may need Admin):
- C:\$Windows.~BT
- C:\Windows10Upgrade
- C:\$Windows.~WS
- %LocalAppData%\Microsoft\Windows10Upgrade
Run cleanmgr.exe → tick “Previous Windows installation(s)” if listed → OK. Frees more space.
Ensure 25GB+ free on C:.
Reboot.
Download fresh Update Assistant from microsoft.com/software-download/windows11.
Run as Admin.

This is the standard fix.

Method 2: Disable antivirus and network optimization

For interference issues.

Disable third-party AV temporarily: open the AV utility → pause / disable.
Windows Defender: leave on (typically doesn’t interfere).
For corporate AV (Bitdefender Endpoint, Carbon Black, etc.): these can be aggressive. Add exclusion for Update Assistant’s install folder.
For network: ensure stable. Disable VPN. Use wired Ethernet if possible.
For Windows Defender Firewall: temporarily allow outbound for setupprep.exe. Add rule.
For SmartScreen: allow execution of Update Assistant. Right-click .exe → Properties → tick Unblock.
For limited bandwidth: Update Assistant pauses on metered. Settings → Network & internet → pick connection → toggle Metered connection off.
Re-run Update Assistant. Watch progress.
For chronic network drops: lower download bandwidth in Delivery Optimization to allow stable speed.

This is the interference fix.

Method 3: Skip Update Assistant, use ISO direct install

For bypass.

Update Assistant just downloads what would be in the Windows 11 ISO. Skip the assistant:
Download Windows 11 ISO from microsoft.com/software-download/windows11. Click Download now under Disk Image (ISO).
Mount: right-click .iso → Mount. Note drive letter.
From mounted drive: run setup.exe.
Pick Download and install updates if internet available, or Not right now for offline.
Pick Keep files and apps. Walk through.
Update completes via in-place upgrade. Settings, apps preserved.
For Media Creation Tool: download MCT from same Microsoft page. Run. Pick “Upgrade this PC.” Same result.
For Settings → Windows Update: built-in update channel. Often works after wsreset and cache clear.

This is the bypass route.

How to verify the fix worked

Update Assistant runs through all stages: download, verify, prepare, install.
No restart-from-zero loops.
PC reboots, completes update successfully.
winver shows new build.

If none of these work

If still loops: Specific KB blocker: Microsoft may block update for your hardware. Check Windows Update history for “blocked” entries. For older PCs not meeting Win11 minimum: needs registry bypass or Rufus modification. Risky. For Insider Channel: switch to Stable. For BitLocker: suspend before update. For storage on slow HDDs: download to SSD if separate. For background process conflict: clean boot (msconfig → Selective startup → uncheck all services from third-party). For chronic update failure: sfc /scannow + DISM repair first. For HOSTS file blocking Microsoft: check C:\Windows\System32\drivers\etc\hosts for blocked Microsoft IPs. Restore default. Last resort: clean install: backup, format, fresh Win11 install.

Bottom line: Kill running Update Assistant processes. Delete C:\$Windows.~BT and Windows10Upgrade folders. Free 25GB. Disable AV. Re-download fresh Update Assistant. Or skip to ISO + setup.exe.