I played around with this today. I verified with the debugger that the flash is put into deep sleep before the call to the main() entry point.
I don’t have another idea on what device to look at next. Maybe I’ll browse the various nrf52840 threads and see if I can find a case where someone changed power usage by 7uA.
7uA might not matter to most use cases, but I feel like I’ve been challenged with a quest. I’ll try a few more options before letting it drop.