Many thanks, Robin! Appreciated your explanation of way to search! Your GitHub link shows that at initial selftest it sets pins to 1 & pullup and checks whether state persists afterwards. In my case the pin returns 0, what causes the error.
Thanks for other questions, ground is common for all elements, Puck is connected through a level shifter (just for a case, a M74VHC1GT125DT1G with grounded control input) and I power a strip with 40 leds via a booster module on MHCD42. All are powered from a Li-Ion, through a 3v regulator (XC6206P302MR) to Puck.
BTW, at initial state the MHCD42 is turned off, so the level shifter is not powered. But I get the error even when I reset on working MHCD42, when the selftest is performed on working level shifter.. And the story is that I see the error only once per 5-10 resets..
Anyway, thanks to @Robin the error logic is clear now, if I find its reason, will revert.