Problem with Tracing wire in Proteus PCB designer
Sometimes there can be little bugs with the Gerber viewers in Proteus. I have noticed a few before. If you ever get problems like this, the best thing to do is to go back to your PCB layout and double check that everything is the way it should be. Then use a proper Gerber Viewer program and upload your Gerber files. Then you will be able to view your PCB properly and see any problems. 

9 times out of 10 if part of a track doesn't render in, it is because of a bug. If the case was that the connection was missed, Proteus will let you know when it does a pre-production check when generating Gerbers.