Usually figures 1,2,3 of chapter n appears as "n.1, n.2, n.3" in main text and in List of Figures (lof) but this format is not respected if n <= 0, in this case figures appear simply as "1, 2, 3" and the correct format "n.x" show up again only when n > 0.
This sets the behavior you see. If you want to change it, just redefine
You need the
Note that neither the standard behavior nor the one you want is, strictly speaking, "better": this is the question of taste. For me "Figure 0.4" or "Figure -1.5" look strange - but if these are your requirements, go ahead and implement them.