The "Action Safe"-frame has 5% (of the complete image width) space on each side, and marks the area that get's cropped of by average overscan.
The "Title Safe"-frame leaves 10% space on each side, and is the area to be used for text- (and subtitle-) placement. If you place it outside of that frame, it's usually too close to the edge of the TV to be read "pleasingly to the eye".
Your subtitles are clearly placed outside of the "Action Safe", so no wonder they get cropped off.