It appears that you are auditing the design check for Design Pass 0. If so, all user reinforcement is removed in this design pass, which is why Existing Reinforcement As = 0. Pass 0 was created solely for the purpose of span detailing. User defined reinforcement may be in excess of what is required and it is not required to extend this reinforcement over the entire span. The Pass 0 design is intended to represent the minimum reinforcement required at the cross section, which is then span detailed in accordance with the selected design code. This is why the user reinforcement is removed in Pass 0.
The Pass 1 design includes the user reinforcement and any additional program reinforcement required to satisfy the code checks, but does not include the Pass 0 reinforcement. The Pass 2 design, which typically include shear and ductility checks, use the cumulative design from Pass 0 and Pass 2. The Final Design Pass includes any rebar designed in Pass 1 and Pass 2 but not less than the rebar required in Pass 0. This pass is intended to represent the capacity based on the final quantity of rebar. For this pass, the Pass 0 and Pass 1 & 2 results are enveloped.
In this case, the user reinforcement is not orthogonal to the cross sections and, as a result, is at a slight skew to the detailed program reinforcement. This skew and small differences in bar size and elevation cause problems for the enveloping discussed above.
Since the user reinforcement is defined as a continuous mat across the entire slab, you may want to disable span detailing by editing the span segments and changing CS (and MS) Span Detailer to “None.” If this is done, you will see that the program reinforcement associated with the Code Minimum check is removed.