Window is resized when moving to other monitor in KDE Plasma

I am using Ubuntu with KDE Plasma 5.27.8 with X11. I have one laptop monitor and two external monitors. The external monitors each have 1920x1080 resolution. The laptop monitor is scaled down to 1280x800 for better alignment. I have different windows open on different monitors, most of them full-screen. Typical full-screen applications are Brave browser, PhpStorm, LibreOffice calc. I attempt to move the windows from one monitor to another by dragging the title bar with the mouse. When I move a full-screen window from one external monitor to the other external monitor, the window is resized to 1/2 monitor height, while the width stays at 100% monitor width. After snapping to the other monitor, the window then covers the top half of that monitor. In the past I also saw a different effect, where a window from LibreOffice calc would resize to a tiny area like ~5x20 pixels when moved to the other monitor, and snap to the top left corner of that monitor. After changing the arrangement of monitors, so that the laptop monitor is on the side instead of below the external monitors, now the windows resize to the scaled width of the laptop monitor. Still, they don't go back to full screen after moving. Questions: - Why does the resize happen? - How can I prevent the resize, and make the window occupy full screen after move? The rule should be: If a window was full screen on monitor A, it should still be full screen when moved to monitor B.