Iv had this issue with the pencil for ages now and tried a lot of different suggestions on various sites but still cannot seem to fix it. I also have the program at work and it works perfectly fine but at home when I go to draw with it I get this weird outline and it doesn’t do anything. I can do things with it but nothing appears when I try and use it. I thought it was windows but if it works fine on the same windows OS at work but not at home something within my downloaded copy of gimp must be the issue and I didn’t find anywhere this issue to find a solution to my frustration. Each new version of Gimp I update to the pencil still seems to have this issue
Not broken. You have the paint tool (pencil / paint…) in a dynamics mode
Go into the tool options and set the dynamic to Dynamics Off
edit: A little explanation.
By default Gimp saves the last settings used.
Gimp keeps the settings in the User profile
The User profile remains between Gimp installations…
…which is why reinstalling Gimp rarely works 
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