It's not just Android, although that's where I it use it most often. Same behaviour happens in IOS. This worked flawlessly until a couple of years ago. As a former software developer, my opinion is that there is clearly something wrong with the search indexing on the client side. The files are there; you can scroll down and find them, but the search function is completely unreliable. The problem is not that it doesn't work at all, the problem is that it only works =sometimes=. Again, with my development background, I cannot imagine how this would be such a difficult problem to solve, if the application provider had the motivation. There are currently 16 pages of posts on this one issue, and considering how Microsoft is aggressively herding their customers to the cloud, one would think they would be paying attention to this issue. They clearly aren't.
In slogging through the forum pages, I don't recall seeing a single meaningful response from Microsoft.
Maybe they should consider renaming this community from "Microsoft Answers" to "Microsoft Unanswered Questions".
I do miss TechNet. It was a paid service, but it was worth it.
Good luck,
Tim