Lead or any other addition like sulphur that forms discrete inclusions in steel is done to improve machinability. However that comes at the cost of decreasing every other property, especially ductility/formability and weldability.
SAE 1215 adds S and P, but not Pb.
SAE 1214 adds all three, which is the horror scenario for everything other than machining.
So yes I think your problem is directly related to the change in material.
BTW if your part carries potable water it should NEVER be made using lead-bearing material.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

Thank you for your answer, i'm going to submit the raw material to a tensile test, but it will probably show its lower ductility when compared to a SAE 1215...

This kind of part are applied for hydraulic oil, so we are safe about lead contamination in water.

Often these free machining grades will look fine in a tensile test, but when you try to bend them and strain them in directions other the "L" you are in trouble.

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P.E. Metallurgy, consulting work welcomed