Crash after creating a new project

What is your operating system?
Ubuntu 20.04

What is your Shotcut version (see Help > About Shotcut)? Is it 32-bit?
20.10.31

Can you repeat the problem? If so, what are the steps?
(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.)
Create a project, add a video file and two images on separate video lanes, add an audio track and put some sound on that, add a filter for resizing and positioning to both images, save the project and export it! Proxies are turned on. Now, create a new project, open a video file, copy it to playlist and from there to the timeline and you experience the crash!

I reproduced this (a simpler way) and fixed it for the next version 20.11

Thank you! What was the reason for this misbehaviour of the software?

See the git log. I do not have time to look up the link for you.

I found the log and had a look at the file Timeline.js. You added an else-case. This is too technical. I am just curious what was the reason for that crash, what went wrong. As you repaired it, you can also explain in layman terms what you did. Because if I knew this software from inside, I could fix things on my own and there would be no need for asking questions like the mine one. This is not a software that I know from inside but I’m still eager to learn from other’s mistakes.

The timeline has a current track denoted with a gold background. As you are dragging something over the timeline, the current track is updated for the eventual drop. After you close a project that had multiple tracks and you drag to an empty timeline, the current track was not updated, and a stale invalid current track index could be used.