All credit goes to a Steam user in the Call of Duty: Black Ops 3 forum. Now keep in mind that some people didn’t find this as a fix and nothing changed, but this is one of a handful of fixes and this particular one was what fixed it for us.
-Go to your Steam folder location and continue going down this path: Steam/SteamApps/common/Call of Duty Black Ops 3 Beta/players
-Once in the “players” folder, open the config file in note pad, find the word/text “WorkerThreads” and change the number from “4” to “2”.
-Save and close / close and save , then right-click the config file and hit properties. At the bottom you’ll see “read only” with a check box next to it, mark it and save.
That’s it. Open the game and enjoy a stutter-less free COD BO3 PC beta experience.