I have noticed that images with captions don’t resize properly when I export a text in MOBI format. Portions of the image and the caption are cut off with certain text widths.
Action shots: Mobi Export
Live demo:
https://mediaspace.wisc.edu/media/Pressbooks+MOBI+resize+issue+July+2018/1_v8m4t54j
The same exported images PDFs and EPUB exports are fine, however:
Epub export (great!)
PDF export (swell!)