Unable to start FUS

I am using the STM32WB55RG MCU, Bluetooth feature with stack version 1.13.0 and FUS version 1.2.0. Everything was working normal until I tried doing the firmware upgrade of stack from v12.0 to v13.0. I am not able to perform FUS related operations. The version reading shows 0.0.0 for FUS. And following is the log when I hit "Start FUS"

 11:09:47 : Warning: Option Byte: nSWboot0, value: 0x0, was not modified.

 11:09:47 : Warning: Option Byte: nboot0, value: 0x1, was not modified.

 11:09:47 : Warning: Option Byte: nboot1, value: 0x1, was not modified.

 11:09:47 : Warning: Option Bytes are unchanged, Data won't be downloaded

 11:09:47 : Succeeded to set nSWboot0=0 nboot1=1 nboot0=1 

 11:09:47 : Memory Programming ...

 11:09:47 : Opening and parsing file: 0x495_FUS_Operator.bin

 11:09:47 :  File     : 0x495_FUS_Operator.bin

 11:09:47 :  Size     : 8 KBytes

 11:09:47 :  Address    : 0x08000000 

 11:09:47 : Erasing memory corresponding to segment 0:

 11:09:47 : Erasing internal memory sectors [0 1]

 11:09:47 : Download in Progress:

 11:09:47 : File download complete

 11:09:47 : Time elapsed during download operation: 00:00:00.272

 11:09:47 : Application is running, Please Hold on...

 11:09:47 : Reconnecting...

 11:09:47 : Reconnected !

 11:09:51 : Reconnecting...

 11:09:51 : Reconnected !

 11:09:51 : Error: FUS_STATE_ERR_UNKNOWN

 11:09:51 : Start FUS failed !

 11:09:51 : Error: Start FUS Operation Failure! Please, try again

Following is OB info attached. Cube programmer version I am using is : v2.9.0

What could be the issue, please let me know how to resolve FUS and start wireless stack successfully ?

Thanks.

Arshiya Tabassum

@bponnanavenkat@actalentservices.com