Your captions have received different paragraph styles, namely Style2 and Style6 which have different “Spacing above” attributes.
If you didn’t create these styles (which is likely considering their names), this is a result of conversion/translation from DOCX to ODF where direct formatting often causes creation of many one-use-only styles.
Documents with graphical material are the most difficult to format so as to achieve what you want. Road to success goes through extensive use of styles, not only paragraph and character, but also frame styles.
If you are eager to avoid formatting nightmare, follow @Hrbrgr’s advice and work in native .odt format. Only this format knows of frame styles. Only this format guarantees stability of your document (preventing loss of information by constantly converting to and from DOCX).
And since you have text which must always remain attached to the images, use Insert>Caption. Study the really cool Writer features in the Writer Guide.
PS: your sample document is plagued with direct-formatting. This will make your life very difficult. You also insert your images As character. Think twice about it. This may be correct if your image is “stand alone” in its paragraph with no other information (in particular, no caption). But since you need a caption, a better solution is to insert To paragraph with a specific frame style, then Insert>Caption and assign another dedicated frame style to the composite object image+caption. This object is anchored to the paragraph you designated and will move with it. Therefore, it illustrates this paragraph text which could contain a description or explanation of the image and you know the image will always be in the vicinity, no matter what happens to document formatting.
