Did some tweaking for you, normalizing audio levels and removing a half-dozen or so gaps, which can cause transition freezes and other misbehavior. To see gaps on video track 1, switch to Storyboard mode.
Download and install this beta version, which has some enhancements over 10.12... https://www.nchsoftware.com/beta/vpsetup.exe
When editing it's wise to play the timeline after every few edits. If things look smooth, save project file AS. Do this routinely, giving it a unique # or name, so as not to overwrite prior saves. Using Save Project Files (no AS) will overwrite.
To access this choice, click the chevron to the right of the SAVE PROJECT button on the toolbar, or click MENU (top-left), then FILE | SAVE PROJECT FILE AS. Then you're protected if things go wrong. Click the VPJ file of choice and, as long as source content hasn't been deleted or moved, the project will load.
When exporting, suggest you change the "auto match" field to 854x480, to minimize export time - or 1024x576 at most. Higher resolution likely isn't necessary and will slow things down considerably.