I've never seen this before, I restarted my server to make some changes in the BIOS and after failing to find the change I wanted to make got this at boot:

The last part that repeated took a LONG time to cycle through and showed no sing of self correcting.

In the end I unplugged the UPS and rebooted without issue.

The screenshot shows what happened. The boot didn't fail because of the repeating messages. Just before them, your Unraid flash drive dropped off the USB bus with read errors, so /boot could not be mounted and startup stopped. After that, the flash drive's port could not detect it again.

The repeating part is the UPS disconnecting and reconnecting every few seconds. The UPS and the flash drive are on the same USB controller. Since the server booted fine with the UPS unplugged, the UPS reconnect loop is the most likely trigger.

I'd suggest:

1. Back up your flash drive now (Main > Boot Device > Flash > Flash Backup) in case it is also starting to fail.

2. Connect the UPS to a different USB port, ideally one on a different controller from the flash drive (for example a rear port if the flash is on an internal header, or the other way round). A USB 2.0 port is preferable for the UPS if you have one. If possible, also try a different USB cable for the UPS.

3. Once the server is up with the UPS reconnected, check the syslog for repeated "USB disconnect" lines from the UPS. Then post the diagnostics zip (Tools > Diagnostics).

If the flash drive drops off again, even with the UPS on a different controller or unplugged, test it in another direct motherboard USB 2.0 port. If it still fails there, replace the flash drive.

Backed up the drive... had to reboot and the drive failed completely. Swapped it out and I'm back up and running.