I'm highly confident it's just an engine's self-diagnostic routine which runs periodically when conditions are favourable Most likely the ECU measures degree of EGR cooler blockage - similarly as the actual built-in test (below). I would say perfectly normal.
So it seems - inevitable P0401.
Well, visited a VW garage to be tested - the van had accumulated 30 events in ECU's memory since July 2021 (since 20 months now). Eventually managed turn on the emission light at event number 31 - thus had a priviledge to have EGR flow tested. The result - pending - the ODIS went to an unending loop without a concluding result.
Meanwhile, I think I have reproduced the EGR flow test using VCDS. However, I don't have any reference value to estimate the degree of EGR cooler blockage. Neither did ODIS tell the reference value (should have told but the computer...