Sophos Flashing Tool starting transfer and hanging after

Hi all,

I'm trying to recover a bricked APX320 AP.

It seems that Sophos Flashing Tool works at the beginning of the connection, I can click the "FLASH" button and I can see from the serial console that the image starts transferring but after a few seconds the transfer is blocked and it's in timeout. 

I've tried several different Windows OS versions , VMs and all behave the same:

Network Configuration is changed for recovery process
TFTP: server started
TFTP: server started
TTP: TFTP RRO opcode from 169.254.12.34:3761
TFTP: Read request. Filename APX.uimage with mode octet
TFTP: Creating file stream.
Done (filestream is VALID)
TFTP: Sending filestream..
TFTP: Transfer stopped

Is there any alternative ? Can I use another TFTP server ?