iPhone 14 stuck in Recovery Mode after iOS update - restore always fai

Hi everyone,

I'm trying to diagnose an iPhone 14 and I'm running out of ideas. I'm hoping someone with board-level repair experience has seen this before.

• Bought a used iPhone 14 on Vinted.
• The battery was swollen and the phone would not power on.
• Replaced the battery.
• The phone started working, but it was kernel panicking every ~3 minutes.
• After troubleshooting, I found that the rear assembly (MagSafe / rear flex connector) was disconnected.
• Once I reconnected the rear assembly, all kernel panics stopped.
• The phone booted normally.
• Face ID worked perfectly.
• I could use the phone normally with no more random reboots.

At this point I assumed everything was fixed.

I decided to update iOS from my Windows PC using Apple Devices.

During the update the phone entered Recovery Mode.

Since then it has never booted again.

It always goes:

Apple logo → Recovery Mode

It never reaches the "Hello" screen.

• Apple Devices
• 3uTools
• iTunes
• Original Apple cable
• Multiple USB ports (front and rear)
• Mobile hotspot
• Google DNS (8.8.8.8 / 8.8.4.4)
• Firewall and antivirus disabled
• Different Windows PC
• Different rear USB ports
• Rear assembly completely reconnected
• All connectors checked and reseated

• Error 3004
• Error 1109
• Error 9 (most consistently now)

The current situation is:

• Apple Devices completes almost the entire restore.
• Around 98%, during "Verifying iPhone restore with Apple", it fails with Error 9.
• 3uTools also fails to restore.
• "Exit Recovery Mode" immediately returns to Recovery Mode.

The phone was fully functional immediately before I started the update.

Face ID worked.

No kernel panics anymore.

No random reboots.

Only after starting the iOS update did it become permanently stuck in Recovery Mode.

Has anyone seen an iPhone that worked perfectly before an update, then became permanently stuck in Recovery Mode with Error 9 during restore?

Could this still be caused by a hardware issue (dock flex, rear assembly, NAND, baseband, etc.), or is there something else I should investigate before assuming a board-level fault?

Any suggestions are greatly appreciated.

Thank you!