Have you followed all the best practice tips from here about using the Zigbee Coordinator with a long USB extension cable to a USB 2.0 port or USB 2.0 hub (and not a USB 3.x port or hub) to get the Zigbee Coordinator away from all possible sources of EMF/EMI/RMI interference? → Zigbee networks: how to guide for avoiding interference and optimize for getting better range + coverage
Anyway, for the Zigbee router firmware use that one from ITead/Sonoff → Sonoff_Zigbee_Dongle_Firmware/Dongle-E/Router at master · itead/Sonoff_Zigbee_Dongle_Firmware · GitHub
As for the Zigbee Coordinator firmware you can either choose to use the 6.10.3.0 version from ITead/Sonoff which is mature and as such is known to be very stable or you can choose to use the much newer 7.3.x.x versions which many have reported as working well but has not yet proven itself.
Any more context? What firmware image you trying to flash exactly and what variant of the Silabs Firmware Flasher are you using? Are you trying to flash a dongle that has a Zigbee Router firmware?
Quick glance at your logs it looks like you might be trying to flash a firmware that is not Zigbee NCP? Are you maybe trying to flash a MultiPAN-RCP or OT-RCP firmware image and perhaps also using the upstream Silabs Firmware Flasher from Nabu Casa?
Silabs Firmware Flasher is not a tool from ITead/Sonoff, and I do not think that the upstream version of Silabs Firmware Flasher from Nabu Casa has support for others than their SkyConnect dongle so think that you need to use a fork like the one from darkxst here → GitHub - darkxst/silabs-firmware-builder: Silicon Labs firmware builder and try flashing just a standard NCP firmware.
Regardless, note that this is not the right place to post logs from Silabs Firmware Flasher, suggest that you instead open a new issue in the GitHub repository from where you got it, or try this SL Web Flasher: