The manual says
the surface is not adjacent to quadratic elements the faces of which belong to a contact surface.
but it seems to work correctly when the surface is faces of quadratic elements and other faces of those same elements belong to a surface-to-surface contact as either master or slave.
This can be a common situation for pretensioning a bolt whose shank has contact with the hole it’s in.
Does anyone know what situations cause the problem it warns about?