Sound not playing correctly on timeline

Hi, I have a problem regarding audio in Flash CS6.

I make Flash animations for a living and have been working with Flash for years. Lately, I have been experiencing a very frustrating issue with the audio on the timeline. Normally (when set to Stream mode), it plays one frame at a time as I move from frame to frame, or when I press Enter anywhere on the timeline it plays until I press Enter again. That's the normal way. However, for a while now, it stopped working properly. When I drag the cursor through the timeline 70% of the time the audio does not play. And when I press Enter it sometimes doesn't play any audio either. It feels like it's completely random and if I insist and try multiple times it works, and then there's no audio again. Sometimes as I move the cursor through the timeline it plays several frames and then there's no sound once again. And this is very frustrating and distracting, since I can't animate "blindly" without hearing the audio.

Is this a common issue? I've been Googling it but couldn't find anything concrete. Does anyone here know how I can fix it? Many thanks in advance!

PS: No ActionScript is involved, sound mode is set to Stream, I am on Windows 8.1, Flash CS6