Edited graphics from library fade in and out; not constant for duration of segment

I've observed two different issues. Currently, I have brief segment involving a library graphic that allows one to edit text/shapes. This starts of bright for part of the duration then fades nearly away then rebounds brighter before reaching its end. I see no controls in the right-hand control to adjust anything like that. I want a constant text block of six words to appear for about 20 seconds, introducing my video. 

On another project, I've had the same library graphic appear, disappear, reappear, etc.

What might be causing these?