When I have a large score (number of staves doesn't really matter actually, it's just way more annoying in that case), sometimes as I make notation changes the lyrics line(s) begin to be pushed progressively down the view with each notation change until they are below the stave with which they are associated. The only way to recover from this is to work exclusively in page down/across views or switch to one of those views and back to continuous view. Super annoying.