If you try to deconstruct something (let's say a chest) with your pickaxe and your mouse cursor happens to be in the area, where the "deconstruction progress bar" appears, it will flicker and slow down deconstruction, because it starts and stops rapidly.
To reproduce, place a building like I did in my screenshot right across the quick bar, start to deconstruct it and maybe reposition your cursor, if it is not hovering the progress bar.
Note that this will only work when zoomed in quite a bit .. or if you have a mod like "Long Read" installed, which actually lead me to find this bug.
