Time and temperature play a roll in Stain Blocker's thickness and settling in the bottom of the can. What you are seeing is some of the fillers coagulating.

This is normal as long as it is soft on the bottom; it does not diminish its quality or effectiveness. You should be able to reincorporate the contents of the can - use a paint mixer if necessary because it is a thick, heavy product. However, you should not see any hard settle at the bottom of the can.