ranger "set preview_files true" does not work

Since quite some time the file-preview-window in ranger stays empty. I.e. it indeed shows up but does not preview the content of text-files. Image preview and .pdf preview however does work. The content of my ranger-config-file looks like the following:

user@computer ~ $ cat ~/.config/ranger/rc.conf
map DD shell mv %s /home/${USER}/.local/share/Trash/files/
# set colorscheme [default|jungle|snow|solarized]
set colorscheme default
set mouse_enabled false
set preview_images true
set preview_files true

**Solution attempt 1:** I even explicitly inserted the line set preview_files true into rc.conf, all tough according to this site , ranger should preview text-file-contents by default. **Solution attempt 2:** According to archlinux the function in order to preview PDFs and images is stored in ~/.config/ranger/scope.sh, so I did some research and figured out by this side , that scope.sh is the script ranger runs when it tries to preview **any** file. I never changed it knowingly, but to be save i did reset it:

user@computer ~ $ rm ~/.config/ranger/scope.sh 
user@computer ~ $ ranger --copy-config=scope

Still the preview stays empty!