this happens to me very often, usually i add to TEXTs a transform effect to make them fading-in and fading-out with a bit of extra scale... one text clip... 4 keyframes (transform) ... first with a scale% high and 0 opacity.. the 2 next without scaling and with opacity at 100.. final one with some scale and opacity at 0%... well.. for some reason kdenlive is automatically **set opacity at 0% on keyframes when i change the position (x,y)** of the text. here a video: