When searching for a term in RH 2020 compiled as Responsive HTML5 some of the search term results are highlighted and some are not highlighted.
For example, a user searched for the word "Service."
First make sure you are up to date with patches. For RH2020 it should be update 8. If you are on the first version of RH2020 there is a bug which means you can't use the Updates feature in the application. This is fixed in later patches. You can manually download from here: https://helpx.adobe.com/robohelp/kb/robohelp-downloads.html
Thank you Amebr. I am using RH 2020 7.46. I will check to see if I can get the RH 2020 upgrade.
You might want to unmark my answer as correct. it's only a troubleshooting step at this stage. 🙂
My site www.grainge.org includes many free Authoring and RoboHelp resources that may be of help.