What version of recovery do you currently have?
The recovery has not been updated for 3-4 years(SRCDATE = "20201123").
It would have been updated when I flashed v8.1 when I had this trouble last time - is there a command to check it? Hopefully I won't need it in future as I've tried that 'Flash Image' selection from the main menu on another box and it worked really well, I'm very impressed. I've had trouble with it in the past hence the need to resort to USB Sticks!