Welcome to RAK forum @EFung_IFS ,
It seems you really did a lot of experimentation on you RAK3172. With regards to your issue, I think the only one missing is fully erasing the chip using STM32CubeProgrammer before uploading a new .hex file. This usually solves unusual behavior specially if the firmware moves from different versions and from legacy-to-RUI3 vice versa.
The STM32CubeProgammer via UART bootloader of STM32WL chip is pretty robust and reliable. I can only experience failure if the chip is already damaged physically/electrically.