Thanks for the detailed report, that's genuinely useful, and I'm sorry Pace let you down.
It's logged and it's my top priority right now. What you're describing (output keeping the first few seconds of audio and then going silent, on both MP4 and dialogue-only WAV) is specific enough to work from, and I'm on it.
Two things would help me narrow it down faster:
1. Roughly how long is the clip you're running through Pace?
2. On the MP4, does the video run full length, or does it stop early too?
I'll reply here the moment there's a fixed build. In the meantime, if you'd rather have a refund than wait, email support@glidevideo.com and I'll take care of it.