Why Judson Scott (Joachim) wasn't credited despite being in key scenes

His agent was not happy with the credit position Scott was being offered and refused the credit position in the contract, although Scott signed it anyway. His agent mistakenly thought he could re-negotiate the credit position, but the producers refused.

https://www.quora.com/Who-are-some-actors-who-went-uncredited-for-major-film-roles-and-why