Lost mouse events on hidden windows on Xfce4 (Server) and Gnome (Client)

[kimberli]

A strange thing I recently encountered that I’m not sure what the cause is is that sometimes (randomly or because I activated a shortcut key combination of some program), the mouse navigation function has lost control.
Although I can still move the cursor across the screen normally, it seems that the (default) mouse cursor position is delayed/frozen, stuck somewhere, or even in the window of the screen on some applications.

When I move the mouse cursor to the 2nd application on the taskbar and click on it, the result is the 4th application on the taskbar (and it seems impossible to left-click to open the 2nd application then; the only way is using the key combination to switch windows from the keyboard).

Or when I switch the window from the Browser (here I use Firefox) to a messaging application (Beeper), I cannot scroll the page with the mouse or interact on the message screen; when I try to do that, it strangely affects the Firefox window (which is sunk below Beeper’s window), similar to other applications.

I think there is a problem with the window manager or mouse events, but I don’t know how to diagnose it??

Strangely enough, it also affects the client (Ubuntu Gnome 22.04), following similar mouse navigation.
At first, I thought the cause was the client side, or worse, a physical hardware error, but when trying to connect to the Xfce4 host from Android, the error was still the same.

Sometimes it disappears and then suddenly comes back in a mysterious way.

Can you give me suggestions on what to do to diagnose and debug this case?

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