What is your operating system?
What is your Shotcut version (see Help > About Shotcut)? Is it 32-bit?
Can you repeat the problem? If so, what are the steps?
if you place an audio sound effect (wav/mp3) inside the timeline, and change inside the property the speed to 0.4x or 0.8x and so on, the play button in preview screen heavily fails to reproduce the audio compared to timeline position.
Audio at 1.00000x instead is played correctly
At rendering everything is correct. The error is just inside the preview box