SUMMARY
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I have a Logitech G700s mouse that shows up as multiple devices (plugged in vs wireless). Its scrolling has been inconsistent & jumpy with the mousewheel -- scroll scroll skip longscroll -- but only when plugged in. I put this down to a hardware problem for quite some time.

Today I noticed that a particular app (ReText) did not have the skips, and so looked into software again. I discovered that I'd set the scrolling speed one notch differently for the two versions of the mouse in system settings. Setting them to the same value fixed the jumpy scrolling in all apps.

I have verified that the same thing happens with the G700 removed and two basic wired mice plugged in.
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STEPS TO REPRODUCE
1. Have multiple mice, or one mouse that presents as two mice
2. Set a different scrolling speed in system settings for each mouse
3. Scroll a page in most apps (firefox, kate, konsole, etc)

OBSERVED RESULT
Scroll is jumpy or has skips

EXPECTED RESULT
Scroll should be smooth but with different speeds

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Manjaro, Wayland
KDE Plasma Version: 5.27.5
KDE Frameworks Version: 5.106.0
Qt Version: 5.15.9

ADDITIONAL INFORMATION
problem also existed in plasma 5.25