1. Elements added to the live playlist optimally should carry the same settings and properties. This includes, though isn't limited to the same available CC languages, same video resolutions (quality), multi-audio settings, and codecs (for uploaded videos).
While mismatching specifications may still allow the Live Playlist to broadcast without playback issues, users connecting to the feed will only be presented with UI options corresponding to the video playing at the moment of them tuning in. The Video Player does not adjust its UI for various alterations during switching videos on a Live Playlist, hence mismatching CC or quality settings may make certain seemingly available options non-workable when clicked.
2. To retain the original CC functionality please refrain from switching on WLC for the channel. As the Live Playlist feature itself is a server-side VOD playlist, it makes use of existing CC where available. Switching on WLC will result in creating closed captioning on the live feed but will also disable any previously available CC