I had an interesting situation where we had failure of a Thule bike trailer wheel and could see where the connection-to-the-trailer design had changed from an earlier version (from the company that Thule bought). The wheel functioned the same, but you could see a clear difference which fully explained the failure. I expect it was a cost optimisation, and we only encountered the failure because we used it very heavily.

Edit: they also failed to honour their warranty commitments, but that was secondary.