We are using LMZ23603 to convert from 24V to 5V7 with 1A max output. We have found a number of boards where the regulator starts at the right output voltage set by the resistors (5V7 - 5V8) but then rises quickly (one minute) to 7V and above. The FB voltage goes up accordingly and the regulator doesn't shut off when reaching 0V86 (I have seen 0V95) as per the datasheet. This happens in boards after some time in the field.
They are clearly damaged but still work in an uncontrolled manner. One thing I noticed from the datasheet is the maximum recommended junction temp is 125C and the thermal shut down triggers at 165C. Our heatsinking is not particularly generous and I'm thinking that maybe it has been running for some time at temperatures in between and damaged. But we have other similar regulators in that board showing no problem. I would appreciate any suggestions on what else to check and how to improve the design.