Trouble with plugins because of the code

The theme is developed following the WordPress theme review requirements, not sure what the Plugin developer is trying to say.
I installed the Plugin with Shell Lite 1.7.0 and it works for me, here is the screenshot:
https://www.awesomescreenshot.com/image/470918/e9e5ac01f144caeaf1e80366a6a21258

hmmm, then it has to be my innstallation. Any idea what to do to fix it??

From what I saw you have a child theme installed, could you try with the original theme and see if the issue is still there?