Model: 

XBR-55X900E

Firmware:

PKG6.2676.0070NAA

Issue Description:

About every 10-20 minutes, the screen will black out for 1 frame. This behavior is most obvious/disturbing when watching content with bright color.

Video reference:

The video is captured using a 60 fps cellphone camera. Content is static kindle book.

Link to the video: https://www.youtube.com/watch?v=UYfDfDx1W2s

While in the video, just pass the 1 second mark, only a black horizontal band at the center of the screen blinked/flashed (limitation of the 60fps camera), in real life, the whole screen goes black for about 1 frame. 

This issue appears when watching:

1. Content through any of the 4 HDMI inports, either 1080P or 4K inputs
2. Content using built in app like Youtube
3. In Standard, Game, or Graphics mode

None of the following attempts fixed the issue:

1. Factory reset
2. Using the firmware came with the TV and *not* update
3. Update the TV's firmware (currently on PKG6.2676.0070NAA)
4. Use external UPS with built in voltage stabilizer
5. Adjusting Picture Adjustment settings like Brightness, Motionflow, Local Dimming and others.
6. Enabling Developer mode, toggling settings in Developer mode.

Attempted hardware repair/replacement:

TV was serviced once, main board replaced, but the issue was not resolved.

A replacement was sent, but it has the same problem.

At the current stage, with both TVs having the same issue, it's very likely to be caused by a software bug instead of a hardware defect. Of course, it also could be a hardware design flaw.

I'd like to cooperate with Sony engineer/developer if additional info is needed in order to have the issue resolved.