This has me stumped. I am pretty confident that I don't have a boost or vacuum leak. I have also check tightened header bolts, up pipe to turbo and turbo to dump bolts. All seem good.

Three ideas...both of the ebcs could be faulty so that mine and the spare that I used to test with may have hidden the issue. My ECU may have a new fault with boost control or the map used to to start the car which had allowances for TGV delete, air pump delete, ID1000 and GTX3076 may have a corrupt setting somewhere.