Why not contact Galano directly - there's only so much speculative info that can be gathered from a forum on such a technical matter.

Chris @ Galano could get to the bottom of this pretty quickly.

I highly doubt it is a wastegate issue - the tuning of the EA888 is based around "requested torque" levels, not target boost levels. If you're seeing a drop in boost, it is because the ECU is limiting the requested torque for some reason or another.