iPhone iOS 11.2.5 Update Failure

[Nekomichi]

Device:
iPhone X (iOS 11.2.2)

I'm attempting to update my iPhone to iOS 11.2.5 via iTunes, but the process fails every time and my iPhone is now stuck at the "connect to iTunes" screen and refuses to boot. When updating, the iPhone will enter update mode as normal, but as soon as iTunes reaches "Verifying iPhone update with Apple" the iPhone will immediately exit update mode and reboot to the "Connect to iTunes" screen and iTunes will display a "Could not connect to device" error, followed by this:

Re-attempting the process after force-rebooting both iPhone and my Mac will yield the exact same result, and iTunes will always ask if I want to restore or simply update (I choose to update without restoring every time). According to Apple's support page, this is what I'm supposed to do in the event of an error 9.

Has anyone else experienced this? Could this be due to Apple's servers being broken and refusing to sign the update, or is there some other reason my iPhone won't update?

EDIT:
Selecting "Restore" will yield the same result, iTunes is nether able to update nor restore my iPhone. Both options will fail at the "Verifying iPhone update with Apple" stage and return the device to the "Connect to iTunes" screen. Attempting to boot iPhone into recovery mode and then updating will also fail in the exact same way.

 

[Banglazed]

Attempt to go into recovery mode and update. On an iPhone X, iPhone 8, or iPhone 8 Plus: Press and quickly release the Volume Up button. Press and quickly release the Volume Down button. Then, press and hold the Side button until you see the connect to iTunes screen. I updated just fine on my friend's iPhone X. Make sure iTunes is up to date.

 

[Nekomichi]

Attempt to go into recovery mode and update. On an iPhone X, iPhone 8, or iPhone 8 Plus: Press and quickly release the Volume Up button. Press and quickly release the Volume Down button. Then, press and hold the Side button until you see the connect to iTunes screen. I updated just fine on my friend's iPhone X. Make sure iTunes is up to date.

I have tried that, with the same end result.

 

[Banglazed]

I have tried that, with the same end result.

On iTunes, run a diagnostic test to verify Network Connectivity test to make sure it pass. Use Apple branded cable and or use a different USB port and try again.

https://support.apple.com/en-us/HT201444

 

[anubis1980]

i had this, make sure you use the original cable and try a different USB port. same happened on my X it took four tries.

 

[Nekomichi]

Thanks everyone, I was able to get there in the end.

After a number of re-attempts, iTunes no longer gave me the option of just updating, and made it mandatory to erase the device and completely reinstall the OS. Even then, it only succeeded after several retries with different official cables and USB ports on my MacBook.

It turned out that at the time Apple had experienced some server issues, so I can't discern if the problem was caused by cable authentication or if iTunes couldn't contact Apple's servers to verify the update.

Nonetheless, everything's back to working order now.