Settings say they saved but then they are cleared.

I am using a child of the Twenty Seventeen default theme. There are no other themes installed on the website. I installed and activated the Piklist and WP Helpers plugins. I assumed that if it says it works on WP 4.8 that it will work with the Twenty Seventeen theme. Apparently, I have one or more plugins that conflict with this. Nothing saves. I get a message that a setting was saved but then the page returns to nothing being checked or filled in (such as replacing Howdy).
Unfortunate because I was hoping this would work. I will delete both plugins and look for something else now.