Character Animator Export has random audio cutouts

I have quite a busy scene, with a puppet, and graphics in the background. When I export my project, everything is fine. The music plays fine, the sound effects play fine.

But there is a narration track, imported from audacity, which randomly cuts out throughout. The playback is fine in Character Animator, but it reliably exports with these bugs. I've tried lots of different things, but it still happens.

The narration track has been cut up using the "Split" tool. Could this be something to do with it?

Thanks.