RN 104 failed to start with "Boot from USB" - no FW update

RN104, 4x4TB, 6.2.5 Firmware

2020_03_15 - Sunday morning at 3am, the NAS disappeared from the network, as expected, as I have a weekly "reboot".

It should have come back online at 4am.

But when I tried to access it next day, it wasn't available, I checked it and found it stuck on the "Boot from USB" message.

Than message was unknown to me, apparently it comes after a failed Firmware upgrade.

That in itself is strange, Automatic upgrade were not enabled, the firmware in use is/was 6.2.5, which is quite old.

Some possibly useful infos about the USB ports on the back.

After Christmas I came back home with two USB drives (a 4TB and a 2TB, both un-powered drives) - the idea was to re-align the directory structure on both the NAS and those two HDs. They appeared as two separate "volumes" and they were perfectly accessible. They were attached at the back of the RN104 for "some time". I say "some" because I cannot remember for how long, but at least a month, so the RN104 must have rebooted on the weekly schedule three or four times.

Then one Sunday, it didn't, the NAS "hang" at restart.

I thought that maybe the USBs drives were taking too much juice and I removed them, and the NAS booted fine.

I think that I did not plug them back in for few weeks until I needed to look into one of them (the 4TB), and I plugged the 4TB in.

I think (not sure) that the NAS failed to start again at the following reboot - if so I would have unplugged the drive again and the NAS would have started as normal: but it might have been plugged in for more than one week, meaning that I am not sure if this was the first time the NAS attempted to reboot since then, or it might have started up another time successfully. Also note that I might have unplugged the lead from the disk, not the lead from the NAS, which is under the desk.

Neither of those drives is self-bootable, they are only (and the have only been) purely data storage, plugged in a normal windows7 Dell.

After the  first episode I looked for precautions on USB use, but i could not see any on the manual.

On the link

https://community.netgear.com/t5/Using-your-ReadyNAS-in-Business/RN104-External-USB-disk-disconnect-randomly/m-p/1162564

I read

“There is a current investigation regarding USB detection on the new firmware. For now, a work around is to reboot the NAS after connecting the USB.”

which could suggest that a RN104 could reboot with two USB disks connected (were theyself powered or USB powered ?), if so, then the problem might have started few weeks ago, when it first failed to reboot with the USB disks connected.

In the last couple of weeks I also did a Balance and Defrag, but I don’t think I went into Scrub: Balance claimed back some space (from 0.9Gb free to 1.1GB free, on a  4x4TB population with 12GB capacity)

Any idea of what could have caused this message?

What can I do to get the NAS to reboot normally again?

I have prepared a USB recovery drive with FW6.2.5, but I am awaiting for comments before using it

Thanks in advance,  Berillio

p.s. I have the  logs from 2020-02-26