The default for Gimp is “Save-all-Tool-Options” on exit. I have long thought this is not a good idea for beginners / occasional users who tend to ‘click-n-wish’ in the tool options and then forget what they changed.
As well as zero opacity, line-art detection enabled ?
As a starter I would go into Edit → Preferences → Tool Options and click on “Reset Saved Tool Options to Default Values” Note in the same place a tick-box for “Save tool options on exit”. Consider that.