I have aslo the same problem with my iphone 7 plus.
actully i am a technician so i decides to fix my phone because its not software issue. Its a hardware problem
# Changed the nand no success
# checked nand pada each nand pad have good impidance
# changed nand eeprom
# checked usb track tristar also is good
# i don’t know what should i do to fix it
# here is crash log
# ( [10:24:21.0016] ==== device restore output ====
# [10:24:21.0016] (null)
# [10:24:21.0016] ==== end of device restore output ====
# [10:24:21.0016] AMRAuthInstallDeletePersonalizedBundle
# [10:24:21.0110] <Restore Device 0000000054D58550>: Restore failed (result = 14)
# [10:24:21.0110] Finished RestoreOS Restore Phase: Failed
# [10:24:21.0110] State Machine Dump, status:ERROR - [state:DFU remaining-cycles:1] -> [state:Recovery remaining-cycles:0] -> [state:RestoreOS remaining-cycles:0 (current state)]
# [10:24:21.0110] Changing state from 'Restoring' to 'Error'
# [10:24:21.0110] State is now set to error
# [10:24:21.0110] Restore completed, status:14
# [10:24:21.0110] Restore Checkpoint Fingerprint: 065B.000E
# [10:24:21.0110] Failure Description:
# [10:24:21.0110] Depth:0 Code:-1 Error:AMRestorePerformRestoreModeRestoreWithError failed with error: 14
# [10:24:21.0110] Depth:1 Code:14 Error:Failed to handle message type StatusMsg
# [10:24:21.0110] Depth:2 Code:14 Error:failed to restore APFS image )