When you say "FALLING" the pulseIn() function will wait for the pin to be HIGH, then wait for the pin to go LOW (FALLING), and then count time until the pin goes HIGH again. If the timeout (default is 1 second) occurs the function returns 0. It is easy to miss a pulse if you spend time looking for other pulses.
If the pulses aren't too frequent you can use interrupts to measure the pulse lengths. This should be ble to catch them all.