If your mouse picks (coordinates) or drawing commands are randomly interrupted, your mouse or keyboard (or their Windows drivers) may be faulty.
AutoCAD may receive different coordinates than you pick, there are additional points received, pick sequences (e.g. in polylines) may get interrupted, AutoCAD may start a command instead of getting a X-Y coordinate, typed characters are different or repeated, etc.
All these types of problems are usually caused by a hardware error or driver error (damaged, colliding with another system component) in your keyboard, mouse or other pointing device (tablet/digitizer, 3D mouse, etc.).
Try to update your kbd/mouse Windows drivers, reset their settings to factory defaults, or replace them physically.
If you need to debug the true input that AutoCAD receives, enter the following LISP command in the AutoCAD command line a press Enter:
Now pick different points - you should get a series of messages starting with "(3" - e.g.:
(3 (2231.96 2606.63 0.0))
(3 (2425.22 2667.03 0.0))
Possible other numbers mean that a different type of input was received (another mouse button, keyboard activity...). For a list of events, see GRREAD in AutoLISP Help. You can end the loop with ESC.