Chapter numbering and figure numbering are two independent sequences. However, there is an option in the caption dialog to “link” figure number to chapter number.
When you Insert>Caption, press the Options button to choose which chapter level should be prefixed to the figure number: [None] for no chapter number, 1 for chapter, 2 for chapter.subchapter, …
To modify existing figure numbers, make sure View>Field Shadings is enabled so that you see the limits of fields on your screen. Double-click on the figure number with gray background. This opens an Edit Fields dialog with a Numbering by Chapter section. Choose the chapter level.
You say you have played with Tools>Chapter Numbering (Outline Numbering was the label in older releases, so mention your LO version in an edit of your question to assert which version you use), you may have disabled the TOC collection data. Make sure that for every level Paragraph Style drop-down menu is set to the corresponding Heading n.
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