When I select the spot healing brush, click the left mouse button and release, the image is corrected. However, if I hold left mouse button and move the mouse across the image, all I get is a series of dots a few inches apart with no correction. All of the settings (brush size, mode, type, etc.) seem to work.
I just stumbled on your issue that you were having myself, with the series of dots whilst trying to heal a line (damaged edge of a scanned photo, I got a series of dots too, turned out to be the spacing in the "size, hardness, spacing, angle" drop down, mine had some how gone to max of 1000%, dropped it to 0% and hey presto I can draw a line again. I hope this helps you and others.