The RX clip was blank on export, and out of sync when the project was built as you desribed. Can't say why at this point, but there's something wrong with that file. It's been reported. Please leave your Google link up for a few days so the developers can access it.
Version 7.5 is ancient. With the latest, try this...
Replace the Sequence RX file with the Produce.mp4 file attached here. Right-click on the video below | Save Video As.
Once that's done, with your project on the timeline, right-click Sequence RX in the bin (top-left) and click on Replace Clip File. Select Produce.mp4
Or follow the instructions in my Personal Message (click the mail folder at the top-right of this forum), where the bad file was replaced with the Produce.mp4 and other suggestions were incorporated.
1. Fades were added at the end of your clip and at the end of the project
2. Music level during your on-cam was lowered and your track was amplified to 125%
3. Video level increases were applied to all clips
Thanks for sharing your work.
Produce.mp4