ranger "set preview_files true" does not work

Question

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!

Answer 1

Finally I found a solution:
I just edited in ~/.config/ranger/scope.sh the case "$extension" in-statement, by adding a new case called txt and every time when ranger finds a file with this extension it shall concatenate (cat) this file of given $path variable to stdout, therefore the preview window works again as expected:

case "$extension" in
    txt)
        cat "$path"