Hi,
I've had this problem with kdenlive before. It happens at random times, once every few months I suppose. The monitor is playing video clips that you cannot see or edit in the timeline. I was editing a video that is 20 minutes long. I look at the thing that tells you where you're at and how long the video is, and it says it's 52 minutes long. I can only see the 20 minutes worth of video in the timeline... but if I click play, it keeps going past the end of the video, plays blank space for several minutes, then towards the end it starts playing some video and audio. Video and audio that you CANNOT see in the timeline, mind you. So now I have a video with a bunch of extra, added on video and audio that I cannot even see in the timeline to remove. I now have to render this video and then edit out all the stuff at the end. Why does it randomly put things that are invisible into the timeline sometimes? This has happened with title clips in the past. It's clearly a bug.... I've tried to search about it a few times and can't find anyone else experiencing this.

UPDATE: I just rendered the video (because I was going to put it into a new one and edit that)... and now I can see the missing items in the timeline so I can delete them and continue editing this video. Definitely a bug.

can be ncie to know what version of kdenlive are you using and on what platform (there was a lot of similar issues last year.. now fixed)