Hi Nardos and welcome to the Club. I've never heard of this problem before, so I'm not sure I can help you much.
It sounds like the head-unit and or amp may have tripped a maximum output limiter. This could act like a safety net in that by limiting the loudness of the head-unit it protects your components from "frying". No blown speakers.
However, I'm perplexed about your unit's working up until the volume hits 30, then drops out from then on. This is the point where you take your ES to your dealer and let them fix it under warranty. Generally speaking, most dealers will just remove the problem components and put a new head unit or amp in or whatever the case calls for.
After you've talked with your dealer, come back and let us know what you found out.
Paul
Good Afternoon
I just got my car back today and it was a open circuit which caused the amp and sub to short. Lexus replaced that and a door speaker under warranty.