This is not the right place to post this you must move this thread to "
Mining support".
Anyway, about the signature error, if you flash it with different firmware or lower than the current firmware it won't work you need an SD card flashing or a tool that can unlock SSH and disable the signature check.
If you want there is a tool that I know that could unlock the miner check this thread on how to unlock it here
https://bitcointalk.org/index.php?topic=5205533.0About your 2nd issue much better post the whole kernel logs here you can find it on the system tab then kernel logs copy them all and paste it here don't forget to put inside the "insert code tag" with icon
#Or you can paste it on pastebin.com and paste the URL so that we can have more insight about your issue.