STM32 Unexpected reset when a GPIO pin gets HIGH
STM32 require all Power supplies (digital and analogue + VBat) to be connected and having the decoupling capacitors. If you did noy connect it the chip will not work correctly. 


  PCB has left the VDDA floating howvere, would that have anything to do
  with this since PB0 is an ADC channels?


Do not make such a assumptions - read the uC documentation.