Why does camera (HTC one M8(s)) go out of focus during video recording?

[Luisa Sapio Schiermer]

As soon as I press the button to record video, on my phone, the camera goes out of focus and I end up with a blurry recording. I've tried to reset the camera settings, in case I made some changes without knowing it, but it didn't help. It's only an issue when recording video. When I take photos there is no problem. The lock focus features is off. What could be the problem? I don't remember it to have always have been an issue. In seems like it came out of the blue at some point.