The product is sticking to the seal face. The product is changing state and becoming a solid. A change in temperature. A change in pressure. Dilatants will solidify with agitation.
Some products solidify when two or more chemicals are mixed together.
Like epoxy glue. The hard face is not flat. Parts get dropped and the worker is afraid to tell the boss. He put the part back in inventory without telling any one what happened. The hard face has been installed backwards and you are running on a non-lapped surface.