What firmware version were you using before updating?
Did you also update your DWC files?
At this point I think you should probably use Bossa to flash the latest firmware directly, and then manually update the DWC files on the SD card.
Use this procedure to flash the firmware: https://docs.duet3d.com/en/User_manual/RepRapFirmware/Updating_firmware#fallback-procedure-2
Use this firmware file: https://github.com/Duet3D/RepRapFirmware/releases/download/3.4.5/Duet2CombinedFirmware.bin
Then update the DWC files by putting the SD card into your PC and extract the contents of this zip file into the WWW folder on the SD card: https://github.com/Duet3D/RepRapFirmware/releases/download/3.4.5/DuetWebControl-SD.zip
When you are all done and connected to DWC, upload this zip file to the system tab in DWC. https://github.com/Duet3D/RepRapFirmware/releases/download/3.4.5/Duet2and3Firmware-3.4.5.zip