Sometimes the touchscreen has a slight amount of lag due to an overload on the system, much like people who need sleep after a long day. Before just replacing the screen, try doing a hard restart by holding down the power button for 10 - 20 seconds or until an HP logo pops up.
If that still does nothing, then part of your touchscreen may be defective; however, replacing a certain part of the screen is extremely difficult to do, so I suggest buying a new screen assembly and using the HP Slate 7 screen replacement guide to help you along. Another option is to contact HP support, inform them of your problem, and they will tell you what needs to be done from there.