My brother is currently having a similar issue on his A3. So we no doubt will be going down these routes, however,
Just putting it out there. We have a 2017 VW Crafter that had all the same symptoms - was passing all the test thrown at it, had no end of parts replaced trying to fix it, passed pressure test after pressure test, only to find it was indeed the EGR cooler, the weird thing is it showed no signs of loosing pressure or leakage, but once we replaced that, it sorted our issue once and for all. The reason there was no signs of a leak is the coolant was burning straight off once passing through the cooler, but still doesn’t explain how it managed to hold pressure IMO.
but yeah definitely worth looking at, as we had 2 garages looking at it, one being a VAG specialist.
