Complex sentence: According to Ryan, no one knows how the kiln door locked or how the kiln turned on all by itself, but when Mr. Kankel returned the next day, he noticed the kiln had been on all night.
Split into simpler sentences: According to Ryan, no one knows how the kiln door locked or how the kiln turned on. When Mr. Kankel returned the next day, he noticed the kiln had been on all night.