ReadyNAS 516: mount-block-root-25e error but USB recovery appears to complete correctly

Hi,

I'm running a ReadyNAS 516 with the latest OS 6, version 6.10.8. After a much-needed dusting out I'm now getting the mount-block-root-25e that other threads have discussed at length and am hoping someone has some insight! What makes my issue unique is that the documentation and other forum conversations seems to be a bit out of date for what I'm experiencing:

Background:

1. Power down was done from the web UI. After unit visually powered down it was given 20 minutes before power cord was unplugged.
2. Dusting was performed outside on a non-conductive surface.
3. I've checked all of the cables on the motherboard to ensure a solid fit and reseated the memory just in case.

Recovery workflow:

1. USB recovery utility was run in Administrator mode on Windows 11 with latest tool related to 6.10.8 and OS in the x86 subfolder. Utility catches this and setup is quite smooth.
2. USB is plugged into the front port (bottom middle). Without any user intervention at boot the unit detects and the LCD says it is booting to it, and eventually returns "Recovery Done" and powers down.
3. After the power down, removing USB and powering back on still returns the mount-block-root-25e error

I've attempted the Recovery steps with 3 different USB and observe the same issue with all 3. I know other forum posts have referenced various USB not being properly detected however all 3 appear to get through the initial boot, Recovery process, and power down within 5 minutes.

I'm at a loss for next steps, I'm hoping someone else has seen this!