My unraid server is behaving in the exact same way, but I have many less drives than @FlowerPower... I have 3 data drives, 1 parity, 1 cache for a total of 5.
My server has behaved this way one time before ~4mo ago, when I lost power and power did not come back on before the UPS was out of juice. In this instance, I bought a new flash drive, recreated my boot drive, and then requested a new license / GUID and all was well. The USB drive is being recognized by Windows and I can manipulate folders and data on it, but when plugged into my unraid server as the boot drive, it notifies me that no boot media was found.
Has anyone figured out why this would happen with less than 12 drives installed? I have some critical scheduled events (plant feedings) being managed by scripts in HomeAssistant that can't rely on me having to be here to recreate a flash drive.
The other issue that seems to be happening is that my server doesn't do a clean shutdown when the UPS is running out of battery... looking for pointers on this as well if anyone has any advice.
Thanks in advance.