Absolutely horrible layout for the flying capacitors C17/18/19/20. The traces are way too thin and long. Those caps should be as close as possible to the IC. It seems like you completely ignored the datasheet.
"The two flying capacitor terminals are to be considered high power switching nodes carrying voltages and currents similar to that on the OUTXX nodes. Care must be taken in the PCB design to reduce both the inductance and the resistance of these nodes."
"The two flying capacitor terminals are to be considered high power switching nodes carrying voltages and currents similar to that on the OUTXX nodes. Care must be taken in the PCB design to reduce both the inductance and the resistance of these nodes."