We don't do any timed waits, all of our waits are for an element or value to appear, but these waits never complete sometimes, non-deterministically. We then added a long 5 min timeout on these waits because we know the test will never complete at that point. It's always fine in manual testing though, and if we don't run the browser in headless mode and watch it work. Very frustrating.

Sometimes the HTTP requests themselves timeout after a few minutes, but this never happens in manual testing either. That's actually the most common issue these days, and this happens non-deterministically too. This is what I meant by "flaky".