Failure starts at the tension lager of the panel edge facing panel #3 at the area of maximum bend. This could be an individual plywood issue, a low moisture content issue, or the result of not stitching the panel #1/panel #2 seam well ahead of stitching to the mold frames, or pushing too hard on the edge to get the panel to follow the mold (I ‘ve seen all of these causes while cold molding boat hulls with three layer 3 and 4 mm okoume). So, if go hear the panel crack, immediately take it out of the mold and put it back on the flat bench and apply a 3″ wide 6 oz glass patch along the outside (tension) surface of that edge of the panel. Put Saran wrap over your patch and weight it down with something straight and heavy like a cement block. After overnight cure fair the edges of your patch particularly at the ends. Then install the panel in the mold. The result can not be detected even if you are bright finishing your camper as I am still planning to do. This repair took me all of 30 minutes and an overnight wait for cure.
I should mention that CLC suggests spraying/misting the panel area with water before bending as a way of preventing this infrequent but heart stopping problem.