I have noticed that this glitchiness only occurs in DIRECT TO PLANE mode and is not present in EGL mode, which runs perfectly. Unfortunately, 10 bit videos do not play in EGL mode because of an error: "error <general>: CEGLImage::SupportsFormat - format not supported: NV15"
In fact, it only seems to be present with subtitles displayed. Old VobSub DVD subtitles are fine but any text based subtitles rendered by kodi seem to cause the glitchiness. I wonder if the rendering the font and the video is just too much for the box. Is there any way to reduce the rendering resolution of subtitles perhaps?