As a result of repeated failures of the generation 1 and generation 2 HPFP, BMW issued a software update which changed the low-end boost and wastegate control to try and preserve the life of the HPFP's for as long as possible (in effect, trying to limit the number of warranty replacements they'd land up paying for).
With generation 3 HPFP now proving reliable and a huge volume of complaints about their software change introducing lag and degrading performance (not to mention a class action suit against BMW recently launched in California), they have finally conceded and amended the latest software to handle boost and wastegate control more similarly to the way it was in older software.
BMW USA issued a press release which acknowleged the turbo lag although steered clear of any admissions in respect of the HPFP, claiming that the change (introducing the lag) was introduced to remove noise (referring to a metallic wastegate rattle noise on take-off) associated with the old setup. Lies, damn lies, but nonetheless it would be naive to expect them to confess their sins in the media.
You need to get the latest software loaded onto the car AND on top of that, you need to get the dealer to configure the wastegate control to original state.
Here is the BMW TIS report that I'd suggest you print and provide to your dealer:
Note in particular that you need them to load software ISTA/P 2.32.1 or a more recent version first. Thereafter: select "Conversions", and then select "Wastegate valve conversion". Follow the on-screen prompts to reinstall the original waste gate operation.
BTW, it is normal for there to be some additional waste gate related noise after the change. This can sound like a metallic clanking. It is a minor trade-off well worth the benefit of nuking the lag.