There are normal two video parts on one video track.
The second part is at the end of the video.
Both parts have an opacity (i.m.c. 30%) and then I blend them by making a normal transition.
And the transition has for both parts the opacity of 30%…
If then the second part is longer as e.g. the audio track, I cut it fit to the end of the audio track.
And then the opacity of the second part in the transition is set back to 100%…
Short: Two parts, opacity 30%, making transition for both, cut of the second part to fit to the end of the video, the transition now has an opacity of 100% for the second part.
And Shotcut then tends to CTD, several times. Until, I do not know, then…, and Shotcut is working again like a charme.
BTW: I also noticed this behavior with Shotcut v.19.04.xx.