This happens for me too, but its not frequent.

As stated above, disable the focus follow mouse is one fix.

If you wish to keep focus follows mouse, then the fix would be to use the PiP hotkey to swap the smaller window with your main window, and then press the right mouse button in that window. The error is infrequent and I like to be able to quickly left-click a targeted AoE on each of my clones so prefer this option.