dock changes size even though it shouldn't
I set dock size to largest, always visible and positioned left. As you can see on the first screenshot, app window is tightly positioned next to the dock, as it should be.
But if I open another app, dock suddenly becomes narrower by, it seems, 3-4 pixels. There's a visible gap between dock and app window now. I would expect that dock width stays the same (largest, as I set it up with slider).
Is there any way to really fix the dock width?
MacBook Pro 15”, macOS 10.15