Why are we getting inconsistent Search results?

Greetings.

We're using the latest RH 2017 (13.0.2.334). We have a very large merged help Responsive HTML5 Help system with about 20 child helps. The largest child is our main (or Core) help with 2300+ topics. The help system resides on our web server. We're in our final week of putting localized help content together prior to our commercial release in about a week, and we're noticing inconsistencies in the search results.

For example, if we type the search phrase "updating the software" (w/o quotes), on my machine, I get 392 results. My colleague searching with the exact same phrase gets 6978 results!

Umm.... why?

I would think we would get the exact same search results given that we're searching on the exact same phrase on the same merged help system. This is very concerning for obvious reasons.