RPi2 USB boot problems, maybe hardware?

Since a recent build/install cycle a Pi2 v1.1 (armv7) has stopped
booting stable/14. The machine uses bootcode.bin on the microSD,
which finds and loads u-boot from the USB mechanical disk. U-boot
fails to find the hard disk. I've not intentionally changed U-boot.
Sometimes repeated power cycles induce the Pi to boot successfully
and I'm starting to wonder if there's a hardware problem.

The serial console reports

*** FINAL System shutdown message from bob@www.zefox.com ***                 

System going down IMMEDIATELY                                                  

                                                                               
Dec  6 07:29:31 www shutdown[61398]: reboot by bob: 
Stopping apache24.
Waiting for PIDS: 1093.
Stopping cron.
Waiting for PIDS: 1078, 1078.
Stopping sshd.
Waiting for PIDS: 1075.
Stopping devd.
Waiting for PIDS: 774.
Writing entropy file: .
Writing early boot entropy file: .
Terminated
.
Dec  6 07:29:36 www syslogd: exiting on signal 15
Waiting (max 60 seconds) for system process `vnlru' to stop... done

Waiting (max 60 seconds) for system process `syncer' to stop... Syncing disks, vnodes remaining... 3 2 0 0 done
All buffers synced.
Swap device da0s2b removed.
Uptime: 14h16m14s
Resetting system ... 

U-Boot 2023.07.02 (Aug 25 2023 - 05:50:16 +0000)

DRAM:  948 MiB
RPI 2 Model B (0xa21041)
Core:  75 devices, 12 uclasses, devicetree: board
MMC:   mmc@7e300000: 1
Loading Environment from FAT... ** Bad device specification mmc 0 **
In:    serial
Out:   vidconsole
Err:   vidconsole
Net:   No ethernet found.
starting USB...
Bus usb@7e980000: USB DWC2
scanning bus usb@7e980000 for devices... cannot reset port 1!?
1 USB Device(s) found
       scanning usb for storage devices... 0 Storage Device(s) found
Hit any key to stop autoboot:  0 
U-Boot> usb tree
USB device tree:
  1  Hub (480 Mb/s, 0mA)
      U-Boot Root Hub 
   
U-Boot> 

The failure to enumerate more USB devices seems odd.

Issuing a reset command, or usb reset, results in a hang.
The red LED remains on. It does seem possible to explore with
u-boot commands that don't involve resetting. For example, the 
usb tree command.

Are there any u-boot commands that might shed light on what's wrong? 

Depowring the Pi and external hub (along with the disk) and letting
it sit for ten minutes allows the machine to reboot hands-off when
power is applied to hub and Pi.

During the successful power-up u-boot reports 
...
starting USB...
Bus usb@7e980000: USB DWC2
scanning bus usb@7e980000 for devices... unable to get device descriptor (error=-22)
5 USB Device(s) found
       scanning usb for storage devices... 1 Storage Device(s) found
Hit any key to stop autoboot:  0 
....

No USB connections were changed between the start attempts.

Once up the machine seems quite stable, building world slowly
but reliably.

Thanks for reading, any suggestions appreciated!

bob prohaska