Chalk paint has the amazing ability to be manipulated. One of the ways it can be manipulated is with water! Before chalk paint is sealed, it can be removed by rubbing with a wet cloth or brush. This is highly desirable for several finishes and techniques including wet-distressing.
This means that, especially on more smooth surfaces, applying a second coat of paint can “lift” the first coat. Why? Because the second coat is wet and the brush is stiff.
You can avoid this by making sure the first coat is fully dry (smooth surfaces may need a little extra drying/bonding time) AND making sure not to overwork your brush when applying subsequent coats.