Velocity results show as zero for a conduit set as a Diversion.
Velocity and hydraulic grade
When modeling a diversion in a conduit, diverted flow (based on the rating table) is passed on to the next downstream element. The GVF-Rational (StormCAD) numerical solver approximates the hydraulic grades (and thus velocities) through a profile of a diversion link with a Gradually Varied Flow backwater calculation based on the downstream HGL. Because of this, the "Velocity" result (which is the average velocity) may not be applicable. Instead, you would refer to both the "Velocity (in)" and "Velocity (out)".
An alternative option would be to change the average velocity method to "simple average" and then the "velocity" result will show the average between the velocity in and velocity out.
Bend Angle and Subnetwork Outfall
Similarly, other calculated fields such as the bend angle (used with certain structure loss methods) and the "subnetwork outfall" are not supported with diversion conduits and will not be calculated.
Another possible workaround would be to use a very short length of pipe for the diversion pipe, and use a longer "real" pipe (not set as a diversion) immediately downstream of it to model the majority of the length of the actual pipe. (since results will be calculated for that element).
Downstream Outfall Flow
In version 10.02.03.03 and earlier, flow from a diversion pipe was not accounted for in the calculated flow result in the downstream outfall. Starting with version 10.03.00.XX (due to be available February, 2020) this will be resolved and the flow will be included.
Modeling a flow split (diversion) with the SewerCAD or StormCAD numerical solver
Velocity Calculations and the Average Velocity Methods in SewerCAD and StormCAD