In ArcMap 10.5.1 using Network Analyst, I have created a service area polygon of 1000m along a road network, with a trim of 50m. In the image you will see where the road is linked around, the inside is filled in (red circles). However I believe there should be a hole in this area as it is outside of the trim and not reachable within the parameters.
Process: After adding the Network Dataset I used the Network Analyst toolbar to create a new service area. I added Facilities, which was one single central point. Within Service Area layer properties I set the Impedance to 1000m, in the direction away from the facility. I chose to Generate Polygons - Detailed with a 50m trim. I also chose to generate a line.
What am I doing wrong here?