Hello,
I made a project with photos, videos and small effects with the latest version of kdenlive 19.08
The project setting was personalized (around to 4K) and I decided to change to HD with same framerate.
When kdenlive has changed settings, the photos on the timeline disappeared, but it said there were always here. I tried to render and the photos are not on the video rendered too.
Is it a bug ? Do I need to do something ?
Thank you.

Changing project settings after you started working is dangerous and lead to problems as you described. The better way is to change the size of the video when you render. In the render settings you can rescale i.e. to FullHD.