RN2304 Slow not working on 6.10.8; stuck on volume syncing when reset to factory

This is a replacement unit, it was shipped with 6.7.3

It was working fine until upgrade to 6.10.8

How do I revert it back to early firmware?  which version is stable?

followed below to reset to factory,

https://kb.netgear.com/27204/How-do-I-access-the-boot-menu-on-my-ReadyNAS-2304-3130-or-3138-storage-system

Tried to follow below to create USB but this RN2304 is not listed,

https://kb.netgear.com/29952/How-do-I-use-the-USB-Recovery-Tool-on-my-ReadyNAS-OS-6-storage-system

Does the display port at the back work? I tried multiple mini display port cables/ adapters.

Thanks,

Alan