What happens is that each contact detection point has a “pinball region” associated with it. One can control the size of this region by changing the pinball radius (Details view of Contact Region). In frictional contact, the way in which pinball region is used is, if the contact detection point sees the associated target surface within the pinball radius, we call that “near-field [open] contact”. If the associated target surface is outside the pinball radius, it is “far-field [open] contact”. You will see these terms when you plot Contact Status results, too. The separation of near- vs. far-field contact has to do with efficiency – instead of doing a lot of expensive contact check/search, if a target surface is outside the pinball radius, we do a lot of quicker checks. The warning about abrupt change basically says that we are going from “far-field open contact” to “in-contact”, bypassing the ‘near-field contact’ completely. If one takes smaller time increment, then we have a tendency to go from far-field open -> near-field open -> in contact, so we don’t see this warning message as often. Alternatively, one could increase the pinball radius size, but that will lead to performance penalty since we will be doing more contact calculations if the pinball radius is larger. It is a trade-off.