How do I get the silicone to adhere properly to the ends of the tiles?

I think I cleaned well after the glue and cement mortar dried, but it still sticks because the sealant shrunk.

The seam on the floor on the floor, height 1 cm, depth 0.5 cm, a cord vilaterm behind the sealant. The seam broke not because of the settlement of the plate, but the sealant itself dried out and broke off at the weak point.