The LEDs are
FMU PWR = Flight management Unit Power
FMU B/E = FMU Processor in Bootloader mode (flashing) or Error (Steady)
I/O PWR = Input/ Output Power
I/O B/E = I/O processor in Bootloader mode (flashing) or Error (Steady)
ACT = Activity (a flashing heartbeat) indicating everything is ok
I’ll get that added to the documentation