One more detail I forgot to mention:

When only the UART2 TX pin is connected (RX left floating) and the boot fails, the serial output shows RKUART before stopping.
This only happens when RX is not hardware-defined; as soon as RX is connected or pulled to a known level, the boot becomes reliable ...

We are seeing exactly the same behavior on RV1106 (Luckfox Core 1106).

On our hardware, UART2 RX (debug console) is not hardware-defined — there is no pull-up or pull-down resistor on that pin, so it is left floating when nothing is connected.

With this setup:

Boot is unstable (~50% failure rate ...

Hi,

Did you found any solutions for this. I am also interested in sleep mode.