These two samples show different slurs in
different prints but the cause is the same.
The squeegee is coming from right to left
and because the mesh is too slack and/or
the pressure/drag is too large, the squeegee
slides the mesh along giving the slur
directly connected to the main image. In
bad cases shown on the left, the squeegee
actually judders up and down, taking the
stencil with it and printing a light ghost of
the main image when it next judders back
into (distorted) contact.