I had the same problem with bilstein PSS struts from day one (bought new), the installation was double checked and I also changed the upper strut mounts.
The problem was solved when I got them out and went back to original struts/springs so I┤m pretty sure the culprits were the bilstein struts.
What I┤ve experienced was clunking noise at very low speeds and when I lifted one corner of the car by hand (balancing it left to right).
It had also some kind of strut stiction because when I lifted, by hand, one corner of the car, the height of that corner didn┤t returned to the initial position (I measured 10-15 mm difference), the strut piston was sticking.
I think that there are other users that experienced the same problem.
I┤ve made a complaint to them and I got a refund.
E90 320d M-Sport | Dakota Terra | Blacklines | Íhlins Road&Track 343F/686R| Swift Thrust Sheets | M3 Front Control/ Tension Arm Kit | M3 Rear Guide Rod and Upper Link Kit | M3 Subframe Bushes | M3 Anti-roll bar Bushes | BMWP Brakes Front+Rear | Goodridge Brake Lines | MTEC V3 |