High CPU Usage and delay for 6 to 7 secs

What is your operating system?
Windows 10

What is your Shotcut version (see Help > About Shotcut)? Is it 32-bit?
64Bit, 21.03.21

Can you repeat the problem? If so, what are the steps?
Add some of video track, then move one clip to another track

i often edit a videos for school which need for like 20 students or more, and everytime i move a sliced clip, it always delayed for 6 up to 7 seconds. I tried on Desktop (Ryzen 5 3600 (16Threads), 16GB, GTX1660 Super, SSD 512) and Notebook (Ryzen 3 2200G, 4GB, Vega 8 (onboard APU), SSD256) and both are the same. i also tried turn on Pararel Processing and HW Acceleration ON. still no luck.

i dont know whether this if this is intended to be like this, or this is a bug on thread managements? or i just missed some steps?

It is a known problem that moving clips between tracks takes a long time on a complex timeline because it must redraw it (same effect as pressing F5).

@shotcut, I read the thread that you linked to and you said a possible solution without doing a total rewrite of the timeline is:

when you drag a clip you will no longer see its image moving under the cursor. Instead you will only see a red outline similar to what you see for the other clips when dragging multiple clips. I am sure someone will complain about that degradation of the user experience.

If done how much of the timeline performance would this improve? Because if your only concern is that some may complain over that change I would say that no one will since the behavior you are describing is basically what many if not most video editors especially proprietary ones do like so:

So how far would the improvements in timeline performance go by making that modification?

Or maybe make it somekind of “shadow”, so when someone drag and drop, ithe “real” file doesnt do anything until user click refresh manualy?

I dont know anything about programming, and im already happy to have this app, but i think the response of this app hopefully can be improve

All the best for Shotcut Team!