Poor curing leads to low bonding strength of AM with the grid wires . This weak bonding helps the buildup of insulating surface between AM & grid and leads to further decay of the structure due to localised heating a the point of current flow thru the wires .  Most important catalyst during the curing is the humidity of the chamber that helps in intermediate hydration reaction to proceed which helps in better cementing of active material with the grid wires .If this is not maintained, only free lead will reduce but bonding will be weak which can be felt during drop test after curing .

Basically active materials shed due to low bonding strength which can be taken care of with right selection of additives 

The symptoms and cause May be as: 

1, When the precipitate is brown, it is shedding of positive active material caused by overlarge charging current or frequent overcharge;

2. When the precipitate is white, it is lead sulfate caused by frequent overdischarge or lead chloride caused by impurity chlorine in electrolyte;

3. When the precipitate is a mixture of brown, white, and light blue, it is caused by impurities such as iron and copper;

4. Physical damage may also cause shedding of active materials.

Other than that what may be the Possible cause.