Cut thru doesnt cut straight

When i use cut thru, even on start box, it doesnt cut straight Down . It kinda
bounces around. What am i doing wrong. The cut goes from Corner to middle of opposit Line .
changing the view Also changes the cut. But even with aligning it doesnt go straight …

Don’t be shy, show us what you mean

If you’re using cut-through mode with the knife tool, try changing your view to orthographic. (5 on numpad.)

You have touch the last ending edge with the knife when cutting just like this in order to not have any glitches.