1 - The original result had a 0.8% force imbalance, which is very small.  With the smaller convergence tolerance, that imbalance will be driven down to an insignificant value.

2 - The Z component of the contact reaction force must equal 250 N because there is no other load path.  Since there are two faces and the normals have an angle to the Z axis, the magnitude of the contact force can be higher than 250 N.