Blank parts of video start black then white

In my video project, I have one audio track and one video track.

The video track has several sections without media.

When I exported the project, the first half of the exported video is what I expected. Plain black during the sections without media. However, nearer to the end of the exported video, instead of plain black, it’s plain white during the sections without media.

Works fine here.
No filters.
Blank spaces are black.
Shotcut Version 18.08.01
Windows 10 Home. 64 Bit