Red indicates that the video may not preview correctly, either because you have added effects OR IN YOUR CASE, the clip’s properties do not match your Project Settings.
Green indicates you have created preview files for those clips and now should preview fine.
Why Premiere created preview files is that those clips maybe are a different resolution? By default “Scale to Frame Size” is turned on (Preferences>General), but it may be turned off for you.
All that said, you should have noticed this when previewing before export.
What are the Properties of the faulkty clips.