This is a long standing bug in navigating the multi-file search results. Very frustrating and common. 1. Open devtools on devtools in a Chromium (from source) build. 2. Shift Control F and type "scope" into the "Search sources" input box. 3. Scroll to the bottom of the results, you should see a disclosure triangle and ScriptsSearchScope.js. 4. Open the triangle for ScriptsSearchScope.js. You should see one result, the rest are hidden below (ok that's another bug, we should see as many results as will fit in the window). 5. Click on the first result. Navigation succeeds. 6. Click on the last result. Expected: navigation to the corresponding line. Actual: The search results panel does something funky. Scroll to top? Second click on last line succeeds. First line of results for ScriptsSearchScope.js click again, suceeds, but the last result again fails. I've not looked at the code, but my guess is that the failing case does partial work, but fails to bring the result in to view. Thus the next click after a failure succeeds even though a click on the same result line might fail at another time. This context-dependence is why this bug is hard to reproduce and why quick testing may lead a developer to think the bug is fixed.
Closing as invalid, as this bug pertains to the old inspector UI and/or its tests. Please file a new bug (https://www.webkit.org/new-inspector-bug) if the bug/feature/issue is still relevant to WebKit trunk.