> Some of the time (maybe 10% IME), the person complaining knows how to fix a problem,

Knowing how to fix the problem shouldn't be a hard prerequisite to raising an issue. I've seen situations where everyone on the team is aware of a problem, but the only people with authority to solve it are sitting around waiting for it to work itself out without their intervention.

Of course the natural thought is "raising an issue constructively isn't complaining", but there's a kind of viewpoint bias on both sides of this. Sometimes people who are too wedded to some idea or way of doing things view any criticism at all in a reflexively negative light, just as some people tend to air grievances as a hobby without a constructive outcome in mind.