I had problems with a cople of RAK3172 in previously running systems which suddenly do not respond anymore to AT commands via UART and do not execute their program. The only way to reactivate them is connecting an ST-LINK/V2 interface using STM32CupeProgrammer and reloading the firmware. Even this is only successful when I perform a full chip erase before.
I suppose this has something to do with the boot mode which might be accidently enabled after a bouncing power source is connected or something like that. I use 10µ and 100n decoupling capacitors and 10k/100n at the RST pin as suggested.
What am I supposed to do with the BOOT pin? I left it floating. Is this correct?
Do you have any other hints how to avoid the problem?