Unfortunately, while Kindle Previewer is the most accurate in terms of previewing your eBook exactly as it will appear when purchased, it has developed that little quirk with image captions recently, particularly if the image is centered (and I do hope they get that fixed soon). The good news however, is that in our testing, and what we've heard from authors, it does seem to be isolated to the Kindle Previewer and the images and captions align correctly when the book is uploaded to Amazon and previewed in the KDP dashboard.
Why are my image captions showing up strangely on Kindle Previewer?
Updated over 4 months ago