A profile of pressurized conduits appears to have a flat hydraulic grade line when using the implicit solver (SewerGEMS, CivilStorm) and the calculated Headloss result field indicates a zero or very low value.
This situation may be due to the dynamic numerical solver partially omitting headloss in favor of stability (for example with supercritical/subcritical mix flow computations.) Try adjusting the LPI Coefficient in the calculation options (Analysis > Calculation Options). The default value is 1.0 but a higher value such as 5.0 will tell the numerical solver to apply more dynamic effects. After doing this, re-compute the model and check again. If a value of 5.0 does not help, try a higher value, up to a maximum of around 12.
Note that this adjustment may result in a less table model and potentially the need for adjustment of other calculation options per the below troubleshooting article.
Troubleshooting unstable SewerGEMS and CivilStorm results using the implicit solver