Volvo d13 cracked piston

Hey guys. Need some help with my truck. 800 000 miles D13 engine 2013 I had the truck in the shop for a valve adjustment, replace engine harness and oil change. Took the truck out the shop and made 400 miles bobtail and 60 miles loaded when the engine went into protection mode. Stopped and the truck was blowing smoke and oil like crazy from the blow by hose next to the oil pan. Only from there. The back exhaust was normal. Towed the truck back in the shop and they took the engine apart. The mechanic found piston nr 6 cracked. What are possible causes for this to happen? Can it be just a coincidence that it happened after i had the truck in the shop?Before i took the truck in the shop the truck was not blowingsmoke at all. The mechanic says probably bad injection timing. I had the engine tuned 40 000 miles ago. Thank you

 

I'm not trying to blame anyone. I just want to find an answer so i don.t rebuild my engine and after a while this happens again. I just talked to the tuner and 2 other separate tuners and all of them said they don.t modify the timing when doing a tune