Highlights section is just totally empty on start. Highlights start popping up again after visiting a page; have definitely visited pages within 3 days (which is the algorithm that I've heard people talk about). I saw this as early as 7/27 (which is when the screenshot is from), but it hasn't gone away and saw it again today (8/15).

I wonder if we're getting 500 invalid highlight candidates from the DB so we discard them all and they're not shown. I discovered on my local build, with a ton of desktop bookmarks imported via sync (for testing), I get 192 InvalidHighlightCandidateExceptions thrown from [1] (I filed bug 1390685 because exceptions should not be thrown often). Chenxia, it looks like we log these exceptions at WARN level - perhaps next time you don't see any highlights, you could rotate the device, grab the logcat, and see how often we throw that exception, if we do at all. Note: 500 exceptions might overflow the full logcat buffer so you might want to continuously write to file while doing this. [1]: https://dxr.mozilla.org/mozilla-central/rev/b95b1638db48fc3d450b95b98da6bcd2f9326d2f/mobile/android/base/java/org/mozilla/gecko/activitystream/ranking/HighlightCandidate.java#163

Chenxia, do you use sync on your phone? I wonder if there's a pattern to when you have highlights appear and when you don't based around sync, given that you didn't have highlights this morning but had highlights after using your desktop browser. Can you think of any potential patterns?

From triage: It is possible that all candidates are not highlights. In this case we wouldn't have any highlights to show. If this happens we want to show a message that highlights will appear "here" -> bug 1388377.

Ahh, removed tracking because it's a dupe. :)