My teammates and I have looked at your question, and we have a few ideas, but we're not completely sure what your workflow is.
SideOfEdge refers to the side according to the direction of digitization. When you "locate" a point on the network, SideOfEdge is one of the network location fields that is calculated and stored for the point. You said that your orders are exactly coincident with the centerline, so I presume you have used some type of procedure to explicitly set the SideOfEdge the way you want it. This documentation explains how points are located on the network.
CurbApproach refers to the side with which the vehicle approaches the location. It refers not to the side of the street but rather to the side of the vehicle. If the driver can only service the order to the right side of the vehicle (ie, they drive on the right side of the road and cannot cross the street), the order's CurbApproach should be set to Right side of vehicle. This documentation explains CurbApproach with helpful diagrams.
Based on your question, we think you have it set up this way, although we aren't sure. Assuming you have your data configured in this way, then the question is why the SideOfEdge setting is changing after you solve the analysis. Is that indeed what you're seeing?
The network location fields can be recalculated and updated at solve time. There are some complex rules about when that occurs, but here are some common reasons:
- You added barriers after the location fields were initially calculated
- You changed the travel mode after the location fields were initially calculated
- You re-built the network dataset after the location fields were initially calculated
If you can tell us more about your workflow, we might be able to help you figure out what's going on.