Titles Intermittently Not Appearing in Preview or Exported Video Files

I'm working on a video project with numerous titles and some of the titles are intermittently and inconsistently invisible in the preview and in exported files.

This is one example:

The Primary Storyline contains the core video content.

A series of connected clips include generator shapes (white boxes that have been positioned and resized using the Inspector) to serve as the background for titles summarizing the primary points presented in the core video.

In this first screenshot (above) the title "Allow the First Coat to Penetrate for 30 Minutes" should appear over the solid white box as a second-level title, but it's not there.

If I lift the title from the storyline, the title remains on the same level and a gap clip holding the Slide In and Cross-dissolve transitions drops 2 levels down, below the Generator shape. When that happens, the title appears.

However, if I delete the gap clip . . . the title is gone, once again:

After initially creating the project and previewing everything successfully, something happens and suddenly the project is FILLED with titles and shapes that are intermittently appearing and disappearing.

The behavior is frustrating - in the example I just gave, the previous and subsequent titles appear without any problems, so I tried deleting the title that's not appearing and copy-pasting one of the titles that works.

As soon as I place it in that same slot, it stops working and shows the same behavior as the originally-non-appearing title.

I've tried scrapping the Project and starting over. Everything seems to be great . . . until suddenly it isn't and the same issues return, sometimes with the titles and sometimes with the Generator shapes and usually with different ones that I had issues with in the previous iteration.

I'm running FCP 11.0 on a M3 Max MBP with 64GB of RAM and Sequoia 15.2.

Does anyone have any thoughts or guidance? Thank you!