This is expected behavior.
Assigning static IP is not the standard way to consume a kubernetes service of type LB with PKS/NSX-T. NCP is the main component and you should use the dynamic IP (picked from PKS floating IP pool) assigned to the kubernetes service. Forcing this IP to a desired value is not supported.
Impact/Risks: Since the IP is not added to allocated IP list, the same IP may get used for any other service like SNAT created by NCP leading to a duplicate IP issue.