Moved to Support. Please post in the correct section next time.
The theme displays the automatic thumbnail for excerpts from the following sources (in that order):
1. The featured image of the post, if any is set
2. The first image that was uploaded for the post (not necessarily the first image inserted into the post).
For your situation, it’s likely that you’ve uploaded that image when you were editing the “Library” page, but you didn’t insert it into the page. However, because you’ve uploaded it and it’s on your Media Library, you can insert it without uploading when you’re editing the “Mission & Planning” page.
Simply deleting that image, and then reuploading it again in the “Mission & Planning” page should fix it.