Is there anything else happening with the audio on that page or with the button? Which version do you have? I tested a button to “Stop” and “Play” and it’s working without issues, i.e. always playing the audio from the beginning, in Lectora 17.1.3 and 16.1.2.
Try to put a short delay on the “Play” action, in case the Stop command isn’t finished before the “Play” comes.