[SOLVED] Can't remove category from the side menu

I have two categories in the side menu: Tagging help&support & Tagging general discussions
which I have tried to remove, but without any success.

They are not in lists: Preference/Tracking/Watched, Tracked or Watching First Post.

Both categories are selected in the Muted list.

I have tried log out/in and also deleted cookies for this site

Nothing works.
How do I remove these two from the Categories menu?

In the left menu, click on the pencil icon left of the header “Categories”.
Then unmark the categories you don’t want to have in the menu.

My first thought was “core parts, you probably can’t”, but then I tried and gone they are after hitting the pencil next to the Category header and deselecting