Welcome to the club
As I understand from your post, the picture gets split suddenly, after you have it already synchronized for a while. This may be caused not by your TV, but by the signal you are feeding into it. If you use a CD player, or MP3 player, there may be skips in playback. Even if you don't feel them while playing music, they may be present and can cause these sudden out-of-sync issues. Another reason may be that you are playing a short audio file in a loop. Video2NBTV converts videos in such a way that the beginning of audio file is the beginning of the first NBTV frame, and the end of audio is NOT the end of a frame. So probably your file ends somewhere in the middle of a frame, then playback jumps to the start, and thus the sync is gone.