There are many reasons why baked goods fall in the middle. Some say it's because the oven door was open during the baking process, while others say the bread needs more flour. I think one of the main reasons fig bread caves in the middle is due to the high liquid content. This is due to the amount of juice in the figs. This is especially the case if you use defrosted frozen figs, which is why I recommend straining the figs before using them. Try adding an additional 1/4 cup of flour to increase the flour to liquid ratio.