The attachment from your original post is inserted here for ANSYS staff to see, who are not permitted to open attachments.
A rubber band is like a spring, when stretched to come distance it generates a force F.
When you want to represent the effect of the force F, each body sees the force F. It is wrong to divide that by 2 just because you are cutting out the band and replacing it with a force.
I suggest you represent the rubber band with a spring element.