Problem using UART bootloader

[ARege]

I am trying to program a STM32L151UC chip which is placed on a custom board using the bootloader and STM32CubeProgrammer. 

The connection sequence goes through a few steps until I get a message saying that the chip is in read out protection mode (which it's not, I can see it when I connect using a ST-Link).

I then get the following message: "Error: READ command not acknowledged at address: 0x40023C1C", from what I read this is the flash OBR address.

and the session fails (see full log from the CubeProgrammer bellow)

12:01:50 : Serial Port COM117 is successfully opened.

12:01:50 : Sending init command: 

12:01:50 : byte 0x7F sent successfully to target

12:01:50 : Received response from target: 0x79

12:01:50 : Activating device: OK

12:01:50 : Sending GetID command and its XOR:

12:01:50 : byte 0x02 sent successfully to target

12:01:50 : byte 0xFD sent successfully to target

12:01:50 : Received response from target: 0x79

12:01:50 : Received response from target: 0x01042779

12:01:50 : Chip ID: 0x427 

12:01:50 : Sending Get command and its XOR:

12:01:50 : byte 0x00 sent successfully to target

12:01:50 : byte 0xFF sent successfully to target

12:01:50 : Received response from target: 0x79

12:01:50 : Received response from target: 0x0b

12:01:50 : size of bytes in the response: 11

12:01:50 : Received response from target: 0x31000102112131446373829279

12:01:50 : Full received response: 0b31000102112131446373829279

12:01:50 : byte 0x11 sent successfully to target

12:01:50 : byte 0xEE sent successfully to target

12:01:50 : data sent successfully to target: 0x08000000

12:01:50 : byte 0x08 sent successfully to target

12:01:50 : byte 0x00 sent successfully to target

12:01:50 : byte 0xFF sent successfully to target

12:01:50 : Sending GetID command and its XOR:

12:01:50 : byte 0x02 sent successfully to target

12:01:50 : byte 0xFD sent successfully to target

12:01:50 : Received response from target: 0x79

12:01:50 : Received response from target: 0x01042779

12:01:50 : byte 0x11 sent successfully to target

12:01:50 : byte 0xEE sent successfully to target

12:01:50 : data sent successfully to target: 0x08000000

12:01:50 : byte 0x08 sent successfully to target

12:01:50 : byte 0x00 sent successfully to target

12:01:50 : byte 0xFF sent successfully to target

12:01:50 : Sending Read command and its XOR:

12:01:50 : byte 0x11 sent successfully to target

12:01:50 : byte 0xEE sent successfully to target

12:01:50 : Received response from target: 0x79

12:01:50 : Sending Read address and its checksum:

12:01:50 : data sent successfully to target: 0x40023c1c

12:01:50 : byte 0x62 sent successfully to target

12:01:50 : Received response from target: 0x79

12:01:50 : Sending number of bytes to be read - 1 and its checksum:

12:01:50 : data sent successfully to target: 0x03

12:01:50 : byte 0xFC sent successfully to target

12:01:50 : Received response from target: 0x1f

12:01:50 : Error: Number of bytes to be be read at address: 0x40023C1C not acknowledged!

12:01:50 : Sending Read command and its XOR:

12:01:50 : byte 0x11 sent successfully to target

12:01:50 : byte 0xEE sent successfully to target

12:01:50 : Received response from target: 0x1f

12:01:50 : Error: READ command not acknowledged at address: 0x40023C1C

12:01:50 : byte 0x11 sent successfully to target

12:01:50 : byte 0xEE sent successfully to target

12:01:50 : data sent successfully to target: 0x08000000

12:01:50 : byte 0x08 sent successfully to target

12:01:51 : Disabling memory Read Protection...

12:01:51 : Sending read unprotect command and its XOR:

12:01:51 : byte 0x92 sent successfully to target

12:01:52 : waitForBytesWritten Error : The wait operation timed out.

12:01:52 : byte 0x6D sent successfully to target

12:01:53 : No response from target received

12:01:53 : Error: Disabling memory Read Protection failed