If this occurs, it might be due to BIN and VDD capacitance are too small. At no load, energy in each survival mode pulse is intended to go to BIN and VDD networks on the primary side of transformer. If the auxiliary winding resistance R_AUX is high, it can be difficult to pass this energy to BIN capacitors, and most of the energy goes to output instead. This results in more survival mode pulses than expected to get energy into BIN and VDD which overcharges Vout.

Solution: Use higher BIN and VDD capacitance to attract energy to AUX side. ~47 uF on BIN and ~22 uF on VDD is a good start.

Higher capacitors at BIN pin C_BIN keeps BIN voltage lower than reflected Vout so pulse current steers to BIN instead of Vout. Higher C_VDD keeps VDD higher so fewer survival mode pulses are required. Low R_AUX allows survival mode pulse energy to steer easily in to lower-value BIN cap.