Smudge tool not working

[steele]

I recently installed gimp to edit my photos. I end up having to blur a lot of licence plates with the smudge tool. however, every so often, the smudge tool stops smudging, and seems to do nothing instead. I was able to fix this issue a couple of times by resetting the smudge tool, but this time it still isn't working. The only setting I adjust on the smudge tool is the size of it.
Any advice would be much appreciated. For reference, I am using gimp 3.0

[rich2005]

Very difficult to say without knowing the operations used before smudge.  It would be better if you posted a screenshot showing tool options and layers.   Just a short checklist then for you to consider.

(1) Brush Opacity - should be 100%
(2) The brush, use a suitable brush. If the clipboard brush is set it might be empty.
(3)Turn off dynamics
(4) Flow, if flow is greater than zero smudge acts more like a paint tool
(5) If more than one layer, are you on the correct layer ?
(6) Long shot, any editing that creates a layer effect. Made no difference here but a good idea to merge all layer effects.
(7) Edit: One I missed, Check the layer mode. Set it to normal.

   

Gimp retains changed settings between sessions. Often a new user makes changes one day and forgets the next.
You can reset to defaults using Edit -> Preferences -> Tool Options then click Reset Saved Tool Options to Default Values then OK

[programmer_ceds]

One more thing to add to Rich's list - if there is an active selection the tools will not work outside of the selected area.