I have a number of RPI3 Model B's that I have set up to boot from USB sticks. Initially, they all booted successfully. Some of them have stopped booting after a (variable) period of time. If I replace the USB stick, they boot again; and sometimes stop booting again.
I initially thought it might be problem with the USB sticks.
Now I wonder if some RPI3Bs are doing something to the USB stick's boot sector (or whatever they have in lieu of a boot sector).
At first I was only using Raspbian, but the same has now happened with OCCU. Both OSes boot into a FAT partition before transferring control to a second Linux partition.
If I take the non-booting USB stick out of the RPI3B and plug it into my Mac, I can see the FAT partition. At a superficial level, the FAT partition looks OK, but I don't know what I should be looking for.
Does anyone have any insights into what the problem might be?