I've been using the same prototype board for STM32 (LQFP48 packages) for years. It has a reset switch and a little slide switch to control the state of the Boot0 pin. But I'm now trying the STM32L433CCT6 (GH248 9R CHN 640) chip. After downloading the program via the UART bootloader (which uses my own custom program on the PC), I switch the Boot0 to low and press the RESET switch - normally the downloaded program would start. But for the STM32L433, it stays in the Bootloader. Longer presses of the reset switch, and it still restarts the Bootloader. The oscilloscope confirms Reset line is working and the Boot0 line is in the correct state.
However, removing the battery and reinserting it and the user program runs fine - and from that point on, fiddling with the Boot0 state and the reset switch, everything works normally. It's not a showstopper - but it would good to know why this is happening.