In a past life I saw this type of issue. We found it was caused by the lead forming we performed. The forming to fit the PCB had the leads being spread too far and the forming stress appeared at the lead as it exited the component molding. We had a large issue when the assemblies were sent through a spray over spray wash system but not in a spray over immersion wash system. From the forming process we changed the strength at the lead entrance and when the assembly was hit by the higher pressure sprayers the water was forced into the part, The PCB design couldn't be altered and we ended up only using the spray over immersion wash process with these parts. After that wash process change we never had another issue with the parts.