Hey, I'm not sure if you've already solved your issue, but I’m replying here because I have the exact same power supply board, and my measurement results are quite similar.

From your measurements, pin 4—which should be the VREF output (5V ±1.5%)—is showing only 0.065V. This suggests that the IC isn't operating, even though pins 8 and 9 (VC and VCC) are at 11.5V.

According to the L5991 datasheet, the device disable pin (pin 14) will shut down the IC if its voltage exceeds 2.5V. Quoting the datasheet: "If used, bypass this pin to ground with a filter capacitor...