There is a good way to triage / debug this using chrome://omnibox.

However, if you've already visited the site and can no longer reproduce it, there's nothing we can do.

Most likely the page didn't make it in the history index that searches by title.  It's limited to pages visited within the last three days, visited 4 or more times (over the last three months), or selected at one point from the omnibox suggestion list (over the last three months).  I'd guess that since you only list three dates from when you found it in myactivity, it just barely didn't make any of those thresholds.

Next time you have a problem like this, try typing the beginning of the URL* into the omnibox (type a lot of it!) and see if it ever shows up.  That'll let us know whether it's an problem that it's not in the index of things we search or a scoring problem.

*if I don't know the URL, open an incognito window, find the URL, and the use that URL in the regular window for debugging

Got it, thanks for the info Mark!

I think you're probably right, that I had only visited it 3 times and hadn't visited it within the last three days. Do you know if the count for total number of visits includes cross-device visits? I'm guessing since we don't really sync all navigations that it's just visits from the current device?

It's interesting to me that we have such a short threshold for the time window there. Maybe I just fell into an edge case with the heuristic, but I know that it felt weird that it wasn't showing up in the omnibox :) Why don't we put it in the history index if you've visited it once over the last three months? Is it just performance issues with that approach?

The thresholds do not include cross-device visits.

(unless those visits are synced.  Those visits are synced only if the URL was selected from the omnibox.)

We put all visits in the history index for matching at the beginning of the URL.  For full-text search of the URL and title, we need to limit it for memory and speed reasons.