I have my panel at the left side. The leftmost border, one pixel wide area, is unclickable since upgrading to 5.10.0. When running diagnostic tools and clicking the problem area, they reveal.. xprop: XdndAware(ATOM) = ATOM xwininfo: Window id: 0x2000044 (has no name) (Moving the mouse just one pixel to the right both tools report "Plasma" as expected.) I work with disabled active screen corners and edges. When enabling active edge either for dragging windows or pushing mouse, the left border starts to work some of the time because it pushes the mouse pointer right by 1 pixel.
I have experienced something similar with the top left pixel of my screen even though there is no screen edge (neither regular nor touchscreen gesture) assigned.
*** This bug has been marked as a duplicate of bug 380476 ***