Performance issue - moving clips between tracks takes ages

What is your operating system?
Ubuntu 18.04

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

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.)

Let me present some kind of performance issue. I have amd 7 3700 u powered computer. It’s not very high performance computer but at least it should be decent for video editing.

When I do copy/paste clips between it goes quite quickly. The same is when I do cut/paste clips. However when I move video clip between tracks it takes age. After placing clip on a new track sometimes it takes even 20-30 seconds before I can do anything. I’m wondering why theoretically similar operation copy/paste is so quick comparing to very similar operation move between tracks. (Everything with the same video clip).

Let me show you a short video presenting this. Here i do 1) copy/paste 2) cut/paste 3) move between tracks. Please observe when the video element in the last case is becoming to have a normal color (which means I can do sth next). It takes exactly 20 seconds. The link to the short video presenting this issue:

Moreover it’s common for all my projects. Sure the more complicated the project is, the more time it takes. I’m wondering why? It looks that there is some kind of very inefficient algorithm. In the video you can also see processor usage in the right side of the screen. It shows more or less about 30% usage. Moreover if after moving clips and waiting for the operation end I switch ex. to web browser, I can normally do web browsing without any significant delay (when waiting for shutcut to finish) which suggest that it’s not the processor performance which is an issue here.

Any idea? I have this since long time so it’s not anything new…

Duplicate of High CPU Usage and delay for 6 to 7 secs

Sorry for duplicating. I haven’t notice this. Do you have any idea how to solve this as this problem is known since long time as I can see? And why cut/paste or copy/paste doesn’t cause those delays?