P3: Somewhat important
6.1.3, 6.2.2, 6.2.3, 6.4.3
Tested on Windows (problem), Linux (Zorin 16, no problem), not yet tested on mac
tested with Dell 2in1 laptop w/ precision touchpad (problem) & logitech mouse (problem), and touchscreen (no problem)
To reproduce, try creating a flickable containing a large scene, for example 8000 small rectangles. (you don't need this many to see a noticeable difference, however), and try scrolling using a touchpad
As you can see in the video, in the exact same scene, scrolling with my laptop's touchscreen works perfectly smoothly, but scrolling with a touchpad causes huge amounts of lag and erratic/jerky scrolling
When I sent a demo of my app to a friend (without the dots at the end, i added that in to make the bug more visible for the video), they were very annoyed by this bug too, they noticed that scrolling with their touchpad was very laggy, but with their touchscreen it was perfectly fine.
Update: I also tested it with a mouse: it happens when sending many scroll events to the app, for example when the wheel is spun very forcefully, or with one of those scroll wheels that can just freely spin, in which it doesn't scroll at all until the wheel stops, and then scrolls by a large amount.
Update 2: To my surprise, it actually works perfectly fine on Linux with a touchpad or a mouse, specifically Zorin OS 12 (derived from ubuntu)
Update 3: Not sure if it's relevant to this, no idea if it's only a problem with linux, zorin, qt, or just my mouse, but after unplugging/replugging in my mouse in Linux/Zorin, my mouse scroll wheel stops functioning in my app only until the app is restarted, scrolling still works fine with other apps, doesn't seem to happen on windows either
Update 4: The mouse scrolling problem in linux seems to have been fixed, was having this problem in QtCreator too, when i accidentally disconnected my mouse, which i did somewhat often, the scrolling would no longer work until i restarted the app, but recently this problem went away, i suppose in a new update.