I have also experienced this problem occasionally. The audio comes back when I restart the app by closing it in my background programs and then reopening it. Unfortunately, if I am in the middle of a session, I lose my progress, but this doesn't happen too often.

Here are some troubleshooting steps:

1. Make sure the volume's on.

2. Make sure the silent switch isn't on silent settings.

3. Make sure you have a good and fast internet connection.

(This may be better suited to the Troubleshooting forums. To move it, click edit and choose "Troubleshooting" on the pictured list).

Thanks 856pm. I have verified all three points you had mentioned. But the problem persists.

I will anyways move this to the Troubleshooting forums. Thanks for helping.