Did you change anything in the meantime - install a new version of Psychopy or change the sound files?
If the behaviour is due to the sound library mistaking your sampling rate, you could edit your sound as suggested in the post you quote:
If you’re planning on running your experiment online, your choice of the offline Python sound library is irrelevant as far as I know. But if the sampling rate is to blame, you may still want to check, because you might get the same problem when running online with the PsychoJS counterpart of the sound libraries of Psychopy.