Essentially changes in typical operation procedures at airlines broke previous assumptions about regular full aircraft power downs, which triggered both the 248 day bug and the current 51 day bug.
It used to be that an aircraft would get a full power down as often as daily, but as individual components got more reliable and external power easily available, it became common for aircraft to not be shut down fully between flight days.
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Essentially changes in typical operation procedures at airlines broke previous assumptions about regular full aircraft power downs, which triggered both the 248 day bug and the current 51 day bug.
It used to be that an aircraft would get a full power down as often as daily, but as individual components got more reliable and external power easily available, it became common for aircraft to not be shut down fully between flight days.