I think spontaneous human combustion is most likely misunderstood http://skepdic.com/shc.html
The more recent examples are interesting, but it is baffling that a person, would combust, and leave little impact on their surroundings, which are usually more flammable than a person.
However, no cases of spontaneous humans combustion have been observed. Which poses the possibility that they where dead and at least somewhat dried out at the time of ignition.
“Almost all postulated cases of SHC involve persons with low mobility due to advanced age or obesity, along with poor health.[14] Victims show a high likelihood of having died in their sleep, or of being unable to move once they had caught fire.”
“The "wick effect" hypothesis suggests that a small external flame source, such as a burning cigarette, chars the clothing of the victim at a location, splitting the skin and releasing subcutaneous fat, which is in turn absorbed into the burned clothing, acting as a wick.” For details: https://artcmr.com/Fire-ex/assets/combustion-of-animal-fat-a...
In other words a dead or effectively immobile person plus external ignition source could look like the human was what caught fire. Rather than a small external fire slowly consuming a body over a considerable amount of time. Further, several similar though slightly different means may be involved.
How do you go from explaining ~95% to explaining 100% and thus saying nothing is unexplained?
For example, 3rd degree burns due to their clothing / bed sheets catching fire but the body is not consumed by the fire.