OK, then there you have your answer.
After 1.5 minutes your power bank switches off for lack of current (even active sensors will be drawing too little for it to detect), sensors lose power, and the Arduino reads zero distance (as the pulseIn times out and returns 0).
Just connect the sensors to the Arduino for power. They don't draw much, not worth messing around with external power supplies for this.
Also, next time use a real power supply. Not a power bank.