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LT3471 Negative Supply

I have designed a ±20V power supply using this device and I have used the same design on a previous board which worked well. This time I am using an increased power supply (from 8V to 12V) and the only other change is the input capacitor was swapped for an electrolytic of the same value. When I tested the power supply the positive side works but the negative side was drawing a lot of current and the output was 0V. I tried a couple different capacitor values at C58 and after a couple tests put the value back to the original value to get images from probing of the switching node however at that stage it completely burnt itself out and I am now measuring 8Ω between SW2 and GND. I can't understand why this circuit worked in the previous design and not in this one. Any advice or indication what is causing this problem would be greatly appreciated.