I've moved this from the Using the Community forum (which is the forum for issues using the forums) to the Illustrator forum so that proper help can be offered.
Does switching to CPU Preview help? (Cmd E or Ctrl E)
What version of Illustrator and what operating system are you using? It also sounds like it could be a redraw issue so it might be helpful for you to check your computer against the system requirements for Illustrator which can be found here: https://helpx.adobe.com/creative-cloud/system-requirements.html. Also, it's possible that turning off GPU performance in Illustrator's Preferences might help.