What is your Shotcut version (see Help > About Shotcut)? Is it 32-bit? 21.09.20 64 bit
Can you repeat the problem? If so, what are the steps?
Import a clip, change its speed in properties, drag it elsewhere on the timeline and it turns out black.
(Please be specific and use the names as seen in Shotcut, preferably English. Include a screenshot or screen recording if you can. Also, you can attach logs from either View > Application Log or right-click a job and choose View Log.)
I found a work-around for this - by opening another video timeline I could edit the videos in that timeline and if I decided I needed to move it I could drag it to the one below without issues.
It did it several times for me while editing a wedding video - the clip does move but no longer works. I just tried it on my Macbook but it works fine. If I manage to duplicate it on my desktop again I will take note of my layout - I had 3 video tracks and an audio track.
I just re-opened that project on my PC and tried several times but couldn’t duplicate the problem.
Working on cars for a living I’ve found that quite often the fault is caused by “The nut that holds the steering wheel” so maybe it was just something I was doing wrong???
Sometimes but other times the software gets into some bad state through many prior interactions. Unfortunately, those are very difficult to retrace. Undo and redo can be major contributors to those sorts of problems.