I basically had the same problem. Runnin 0.8 bar..
Realised after a while, the boost tee opens up a bit. As in, i recckon the hole gets a tad bigger, so you end up running more boost than previously set.
I noticed after a month or two, that the boost went above the 0.8 bar to 1 bar. Had huge flat spots, and was just shit..
So i turned my boost down to 0.65-0.7 bar, and seemed to worked well.. No flat spots at all
But then again, all i got is, full exhaust, pod.. basically everything else is still stock..
Running rich will also contribute..
Best to get your car tuned if you can afford it..
Let me know how you fix your problem..