I did not have access to a compression test equipment, so I checked what I could with leak down and endoscope. I haven't checked the oil vapor separator yet, but would be surprised if that could freak out suddenly at 5500 rpm and relatively high boost after having driven the car for 25 minutes and roughly 2 hours in total since I brought it out from its rest. In theory, the oil that has been flushed through the system after this event could have been what accumulated in the intercooler at this sudden burst and then just been portioned out in small amounts.

What I think is: At least cylinder one's rubber hose has leaked and caused slow response, hard working - loud sounding turbo charger and causing high back pressure since the waste gate has been kept closed to deliver all that air that has been pumped out through the leak. Idle problem at hot engine indicates that there has been a leak. I had a similar problem before when an EGR gasket was missing. So, when I gradually raised rpm and load it came to a point where the cylinder pressure reached a high level while the exhaust back pressure escalated as well as the internal EGR level (hot residuals not scavenged), which all together caused severe knocking at the hottest point in the cylinders - between the exhaust valves on the squish plateau. Yes, the engine has a knocking sensor, but the ignition retardation strategy is probably a poor protection against such a massive local overheating at high load. The pressure amplitude from knocking can reach several hundred bars and is moreover amplified in between piston and cylinder.

I have two engine failures in my Lotus Evora S behind me, which were caused by high rpm knocking breaking the piston between first and second ring making the compression ring to collapse. All this was caused by a melted pre-cat that blocked the exhaust flow. The second failure was caused by the authorized workshop who replaced the engine and did not check the main cat, which were melted as well in the first failure

I do not think that something that radical has happened to my Q4 since the liners looks fine and there has been no mechanical rattling, but minor ring or piston damages could cause severe blow by which at high load create huge crankcase pressures. Then you have oil all over the place

So, lessons learned. Drive the car more often so that you know what it should sound like!