SUMMARY
For some non-KDE applications that can be dragged from the menu bar (or other window content), the window can suddenly jump to a different location when dragged.

I observed this behaviour with VLC, SMPlayer and Libre Office on KDE Neon user and testing 20220118 and openSUSE Krypron from today (and a similar issue on Tumbleweed, see below).

STEPS TO REPRODUCE
1. Play a video with VLC or SMPlayer (it is important to play a video, the bug may not occur otherwise).
2. Left-click and hold the menu bar (in case of SMPlayer the video region can be used as well).
3. Drag the window.

OBSERVED RESULT
The window suddenly jumps to a different location so that its top left corner is now under the pointer. It may also happen that the leftmost menu opens either together with the jump, or without.

In openSUSE Tumbleweed (Plasma 5.23.5) the issue is a bit different: instead of the jumping window we have a jumping mouse pointer. The pointer suddenly jumps to the top left corner of the window, whereas the window itself stays where it is.

EXPECTED RESULT
The window should smoothly follow the mouse pointer when dragging. Neither the window nor the pointer should jump to a different location.

REPRODUCIBILITY
In principle the problem is always reproducible, but not always with the same applications on the same distribution, so please try all of the three mentioned above if you don't see the problem immediately. E.g. Libre Office 6 seems not to be affected on Neon in contrast to Libre Office 7 on the openSUSE systems.

SOFTWARE/OS VERSIONS
Linux: KDE Neon user or testing 20220118, openSUSE Krypron or Tumbleweed from 22.01.2022,
KDE Plasma Version: 5.23.90 (5.23.5 in Tumbleweed)
KDE Frameworks Version: 5.91.0 (5.90.0 in Tumbleweed)
Qt Version: 5.15.2

ADDITIONAL INFORMATION
The Problem with the jumping mouse pointer first occured mid-2021 if I remember correctly. The jumping window case only happens in the current testing version of KDE.

Note that the problem doesn't show up if the window is dragged by the title bar.