Might be a graphics glitch. Sometimes the graphics card gets data that it does not know what to do with and then you can get weird artifacts. It might be something in one of the elements (or an interaction between elements) that has something that causes these artifacts.
Try the following (on a backup/copy of the project):
-Start removing elements from your model and see if issue dissapears.
-When you know which element it is, try to modify/rebuild/replace it and see if that solves the issue.
-If it is a graphics glitch updating (graphics card drivers, OS, Revit) also might help.
-Test it on another computer and see if same issue present
Louis

Please mention Revit version, especially when uploading Revit files.