I have had a similar problem lately. Intermittent Image Tearing in all Hikvision direct to disk recording (15fps, Iframe at 15, Video buffer at max of 20MB). Same cameras viewed with a VLC rstp stream shows no issue. My non-direct to disk cameras also showed an issue where they briefly paused every second in a recording.
I am using
BlueIris 4.4.2.0 now but reverting back to older 4.4.x versions or late 4.3.9 versions did not help. Also reducing CPU loading by going down to just one camera did not help. All cameras are on a direct wired Gigabit Ethernet (although of course the cameras only use 100m mode). The computer is Windows 10 with an Intel 5th gen i5-5250U CPU, 8GB ram, SSD, supports Intel Quick Sync, latest Intel released video driver.
The workaround for my direct to disk "tearing" and non-direct to disk pauses was to disable HW HD video decoding. The issue shows up when the "Intel HD Hardware Acceleration" Default was set "Yes (H.264) and each camera had the hardware decoding set to "default" (Note: I kept "Also use for BVR for playback" Off always, since it causes other issues).
Now I have each camera's "HW Decoding" set to "No" and the tearing is gone in direct to disk recordings, no pauses every second in non-direct to disk recordings , CPU usage seems higher though, it would be nice if HD decoding would work. Possibly this is an issue with the latest Intel HD 6000 graphics driver? Currently using Intel version 20.19.15.4463 dated 5/25/2016 (I also tried one older version and the latest beta version, no change in behavior)