If anything is stripped or defective on the coilover you need to photograph and document and contact Z1 as soon as possible
Their support has been . . . up and down.
If they don't help you with parts replacement, you can contact Feal directly. They are in California:
https://fealsuspensionstore.com/
I don't know based on your posts if their is a hardware issue, a problem with the car, or a problem with the installer(s)