Your connecting lines are very thin. I would make them at least 2 pixels. You did not give any workflow details, so I have no idea how you set up Plexus. Without a screenshot of all the modified properties for Plexus, it's hard to figure out where the problem lies.
There have been updates to Plexus since Multiframe Rendering (MFR) was introduced as flicker issues were reported. Ensure you have the latest build of Plexus (3.2.6) and try disabling MFR as a last resort. HTH