My Patch Tool brush is not working. It allows me select but then it freezes and the program will not me go further, I I then have to undo my steps until I reach the point right before selecting the patch tool. How can I fix this bug?

It allows me to select the area to be fixed but then it freezes and the program will not me go further, I I then have to undo my steps until I reach the point right before selecting the patch tool. How can I fix this bug?