Patatobear

Major flaw with the avatar "the following component types are found on the avatar and will be removed by the client: mesh collider"!!! To fix your issue you will have to navigate in the Hierarchy from Combine Assasin>Armature>GameObject>PrimaryEffects>pistol fire effects>Shell Ejection, then scroll down to find the MeshCollider and remove it (don't disable it remove it completely). Make sure to do this again to the path Combine Assasin>Armature>GameObject 2>PrimaryEffects>pistol fire effects 2>Shell Ejection. Hope this helps!

For anybody that experiences the same error as DarthNox "the following component types are found on the avatar and will be removed by the client: mesh collider"!!! To fix your issue you will have to navigate in the Hierarchy from Black Mesa Assassin V2>Armature>GameObject>PrimaryEffects>pistol fire effects>Shell Ejection, then scroll down to find the MeshCollider and remove it (don't disable it remove it completely). Make sure to do this gain to the path Black Mesa Assassin V2>Armature>GameObject 2>PrimaryEffects>pistol fire effects 2>Shell Ejection. Hope this helps! (I have based this solution on a similar model from the same maker with the same problem the Combine Assasin, I hope the paths are similar)