Sorry, circuit is in Frtzing but has nothing to do with the issue.
Power is controlled via a NDP6020P, reset via a digital pin + Schottky diode and this is working for quite a while.
Used ceramic 10uF to 22uF throughout the power nodes (18V, 12V, 5V, 3.3V and 1.8V)
Appreciate your interest, but this is clearly a software issue.