If you use %1 in text of a string meter to refer to a measure then it creates no height for this meter unless it is updated even though the text appears without an update.
Try adding DynamicVariables=1 to your meter. The reason is because the NowPlaying measure is threaded and is querying the player for it's data. Sometimes there is a delay is retrieving the data requested, and the meter will have already calculated two "empty" lines.