For the Mastodon Android app, I also sometimes see crashes that make no sense. For example, how about native crashes, on a thread that is created and run by the system, that only contains system libraries in its stack trace, and that never ran any of my code because the app doesn't contain any native libraries to begin with?

Unfortunately I've never looked at crashes this way when I worked at VKontakte because there were just too many crashes overall. That app had tens of millions of users so it crashed a lot in absolute numbers no matter what I did.

Well, vendors' randomly modified android systems are chock full of bugs, so it could have easily been some fancy os-specific feature failing not just in your case, but probably plenty other apps.

Usually I'd just look at clusters of crashes (those that had similar stack traces) but sometimes when you're running a very small % experiment there's not enough signal so you end up looking at everything. And oh boy was there a lot of noise.

In an app with >billion users you get all kinds of wild stuff.

Bugs in the system libraries?