Broken back glass

What would cause the back of Apple 13 Pro to break. Found this am on nightstand with back cracked all over. Phone is 5 weeks old! Has never been removed from Otter box case recommended at purchase. Cracks seem to start around magnet ring and radiate outwards. No drops. Front glass fully intact. No evidence of drop or damage on clear case corners or back. It was fine yesterday and a hot mess was this morning. Heat from outdoor heat wave to indoor air conditioning? What gives? Anyone else?