22psi sounds very high, does it hold that over 5k rpm or is it spiking to 22 on primary and then managing boost better when the secondary comes in? what boost is it holding at 6k rpm?
Regardless of if its been tuned or not Its going into limp mode, when the ECU detects too much knock and cant sort it out by pulling timing the ECU will cut boost to wastgate spring - 7psi.
Mine would do this in its TT japan spec tuned state when i lived north and only had 95. it will stay limited until it goes a certain time without detecting knock, so if you take it for a polite cruise or reset the ECU by disconnecting the battery it will come right, but 22 is way too high on those twins, those lil turbos will just be thrashing hot air, possibly be better off on less boost with a more dense charge. Seen good results on these running 17-18 psi with a tune. without a known good tune stick to 14psi imho