The Toolbox can fall into state where it does not display some items, some are duplicates and some can be disabled.
Sometimes the only remedy is to let Visual Studio rebuild the Toolbox from scratch.
To do that, right-click on the Toolbox window and select "Reset Toolbox".
Visual Studio will go through all the installed packages and reloads components into the Toolbox.
If this won't help, you can perform hard reset of the Toolbox.
Exit Visual Studio and delete all .TBD files in the following folder:
It should be up to four files:
Once removed, start Visual Studio again.
After showing the Toolbox, all items should load instead of loading only the cached versions.