After a couple of journeys with no problems, the EPC light came on again today, as soon as I put my foot down to overtake someone. The car went into "limp" mode as before.
I left the car for 20 minutes while I did my supermarket shop, and it was fine on the 10 mile drive home. No warning lights, performance was fine, but more traffic meant I didn't get a chance to push it hard, just hanging back from the car in front, and a bit of welly to catch up again.
I plugged in my code reader. Unfortunately the Superb 3 isn't in the database (it's quite an old reader), so I only have the "generic" code - P00AF.
A bit of googling suggests that this is a turbo wastegate issue.
A bit more googling suggests that it has become a common issue with VAG cars that haven't been used much during the pandemic - often the wastegate linkage gets stuck, or sticky so it's slow to respond.
Being "sticky" seems to fit with what's happening with my car. Boost is perfectly fine if I roll on the throttle progressively, but it goes wrong if I push the throttle hard enough to drop down a couple of gears.
I found some pics showing where to spray some penetrating oil on a Golf with 2.0 tsi engine, but I can't find the offending part on my Superb. I guess it's hidden a bit further down, under the turbo somewhere.
Looks like it's a trip to the indy.