Try increasing the threshold of the cameras. The threshold can be adjusted in Nexus, and helps differentiate between the retro-reflective markers and noise like glasses reflection. I believe 0.2 is the recommended setting when collecting at 200Hz, but try increasing it to the point where just markers are identified. I had a similar issue and the VICON rep suggested staying within the 0.2-0.5 range. You can reach out to them for help too.

Cheers,

Ryan Alcantara