How to fix python operators disappearing in new Blender files? I'm working on an add-on, frequently reloading scripts and using it to work on multiple files. After a while, doing that, Blender stopped registering some new operators, while it did recognize others. 

The add-on's code had no errors, and nothing would show up in the Blender console.

Here's a picture of the problem: both are in the same version of Blender, with the same version of the add-on. In one file, the operator is available, but not in the other.
Turns out the issue comes from the userprefs file. It can be found next to your add-ons. On Windows, it's in C:\Users\YOUR_USERNAME\AppData\Roaming\Blender Foundation\Blender\VERSION_NUMBER\config. 

Just delete userpref.blend and the issue should be fixed. This will not affect your keymaps and your startup scene, which are stored in another file. But it will reset the User Preferences to default settings.