I too am having the same issue as above. turning off windows fx and turning back on resolves for awhile as stated above. Noticed specifically after windows 10 update to version 1511 (build 10596.29)
fresh install windows fx v6.01 beta also seeing this on a mobile workstation same build using windows fx v6.0
this was a new windows 10 pro install originally then applied all the latest updates.
this is a highly powered workstation, 2.4ghz (8 cores), 24gb ram, nvidia k4200 (4gb) video card