In this scenario, one of the reasons you may not see the code coverage highlighting is that the 'Store Only Aggregate Code Coverage' option under 'Apex Test Execution' is checked. Make sure to option is unchecked.
From Setup, enter and select 'Apex Test Execution' in the side search bar. Then click the 'Options' button. Uncheck 'Store Only Aggregate Code Coverage' if currently checked.
000386084

We use three kinds of cookies on our websites: required, functional, and advertising. You can choose whether functional and advertising cookies apply. Click on the different cookie categories to find out more about each category and to change the default settings.
Privacy Statement
Required cookies are necessary for basic website functionality. Some examples include: session cookies needed to transmit the website, authentication cookies, and security cookies.
Functional cookies enhance functions, performance, and services on the website. Some examples include: cookies used to analyze site traffic, cookies used for market research, and cookies used to display advertising that is not directed to a particular individual.
Advertising cookies track activity across websites in order to understand a viewer’s interests, and direct them specific marketing. Some examples include: cookies used for remarketing, or interest-based advertising.