STM32: Minimal USB bootloader circuit
Can't comment so putting here as an answer. AN2606, page 15 states:


  If DFU is used to connect to the bootloader: the USART1_RX (PA10),
  USART2_RX (PD6) and CAN2_RX (PB5) pins have to be kept at a high or
  low level and must not be left floating during the detection phase.


Also BOOT1 shall be tied LOW (page 8).

USB DP shall be controlled by MCU - bootloader sets USB DFU Device mode so pullup R should be unnecessary.