Just last week, I blew up a perfectly good PSU module when it was installed on the board.
Upon removal of module, I noticed a *very small* dendrite running from the output (170 V) to the adjustment terminal.
Thoroughly cleaning the dendrite and replacing the PSU with a good one, completely fixed the problem.
I'm not saying that your problem is identical to mine. Rather, that these very weird failures sometimes are related to board or solder defects.
This is not the first time it has happened to me. Once I had sensor which was giving intermittent results. To make a long story short, I found that by pushing the board in certain areas, the problem would come and go. It turns out that the board had an intermittent via.
I've several stories like these. And don't get me started on soldering issues of leadless IC packages!!