I haven't heard of any official complaints either.
Interpretation isn't easy work, as Mr. Lymburner said. Interpreters constantly have to rely on their judgment to determine what they can or can't interpret. I can assure you that all interpreters are keen to do their job when they show up for work. They don't enjoy interrupting someone's remarks or saying they can't interpret them because they can't clearly hear them. I can confirm that they don't like doing that.