Its well known that there were tolerance problems with the mech hanger, – the chainstays have been redesigned. All new models have the redesigned ones and YT are replacing any existing ones promptly.
Basically, its down to teething problems that are now sorted.
Yes, that was one of his cracking issues. The other was the front triangle, around the linkage.
He’s since found other people who have found cracks around the head tube too, along with others who have complained about cracks around the BB area.