JCS has.
However the only way that anyone could comment on what actually is occurring with a specific phone would be for the phone to be sent in for examination and the OP is understandably hesitant to do that, particularly as this may be a never-to-be-reproduced problem. If it started happening regularly, I imagine that the OP would be more amenable.
I guess, against that, for those like me saying “read the schematics”, I am not aware that the schematics have been released for the USA Editions and AIUI it is a USA Edition that we are talking about.
The situation remains that for the Librem 5 vanilla edition, the design is unarguably a hardware switch (multiple AP2281 load switch chips scattered throughout the design). No possible software malfunction can interfere with that. (You can easily find the datasheet for the AP2281 on the internet.)