Had a 2c57 with 2cb3 on n18 mini for quite some time now.
Changed diverter valve and inspected wastegate with borescope through the o2 sensor hole and there is a little play but it looked like normal amount compared to videos I saw online. Tried to pull vacuum on wastegate actuator with simple hose and large enough syringe to test the wastegate movement but there was no resistance whatsoever. Today finally replaced the actuator and set the screws on the rod at exactly the same distance as the original and boost is back!

OBD2 Gauge I’m using to monitor coolant temperature is also displaying MAP sensor boost and it spikes at over 21psi. Not sure how normal that is but car runs great now and there are no codes showing up.