It is very important to never let the stencil remover dry. It locks the stencil in the mesh with a permanent chemical bond.

Under exposed stencils are harder to remove than completely cured/exposed stencils.

Under exposed means some of the sensitizer did not cross link. This is always on the inside of the stencil because invisible UV energy didn't have enough time to move all the way through the stencil to the inside. Penetration of UV energy is not 'linear'. The deeper the UV energy has to penetrate, the longer it takes based on the physics rule called the Inverse Square Law. If you double a distance energy has to travel, it takes 4 times the energy - NOT double. Many low energy UV lamps may never penetrate a thick stencil.

When you spray stencil remover on the stencil, it has to penetrate and attack the chemical crosslinks formed by UV exposure. No crosslinks - no easy stencil removal.

The stencil remover chemical creates another reaction with under-exposed stencil and forms a chemical bond with the mesh that is very difficult to remove.