You connect the HC-05 with the Arduino directly with the Tx-Rx line. HC-05 is supposed to be driven on 3.3v and not 5 volts. Your Arduino Tx pin will supply 5v signal on the HC-05's Rx line which is above the recommneded level. Try putting a voltage converter between the Arduino Tx pin (5v) and HC-05 Rx pin(3.3v).
Maybe there is internally a protection that resets the microcontroller inside HC-05 when voltage goes above 3.3.