Lead free solder
I am surprised the official report does not tell us what sort of solder it was that cracked. It is well known that lead free solder is brittle and more easily cracks under fatigue loading than the old leaded solder. I have personally repaired many electronic items with cracked lead free solder (although not avionics as it’s not my field).
In space applications lead free solder is banned, although I think that is more to do with tin whisker growth in a vacuum than cracking.
The banning of lead in solder may have saved the odd life from lead poisoning but the loss of life in this accident more than outweighs it and a relaxation of the requirement for safety critical applications like avionics would I am sure hardly affect the rate of lead poisoning, as the volume of avionic products turned out is far less than say consumer electronics. Or do avionics already have such a relaxation?