I find that the problem is in the U2 because your output is not gradual in the input - of u2 i have 10,5V and the input + i have 0V to 11,3V q2 and q4 is OK
the output of my power supply remains always in 30V the input+ of U2 have regulation of 0,3 - 11,2 V but your output remains in 30V sorry for my English but i'm from brazil and my English is very bad ;D
i'm from brazil sorry my english, but i built the power supply and in the out i have only 0 to 9,3V i test all but i don't know what i can do help me please :)