I’m running into issues with my AI character behavior. When I drag the prefab directly into the scene through the editor, everything works perfectly. But when I instantiate the same prefab through code during gameplay, the AI doesn’t work right.
The main problem is with the ThirdPersonCharacter component on my AI. Instead of playing the walking animation, it just stays in idle mode and slides across the ground to reach its target. I traced this back to the CheckGroundStatus method where this line causes issues:
animatorComponent.applyRootMotion = false;
It seems like the ground detection isn’t working when the prefab is spawned at runtime. The character can’t tell if it’s properly grounded, so the animation state machine doesn’t transition to the walk state.
I’m using Unity’s standard AI character setup. Any ideas why the exact same prefab behaves differently when spawned through code versus placed in the editor?
Had the exact same sliding issue last month. It’s usually layer masks getting messed up on runtime spawned objects. Unity handles everything fine when you place prefabs manually, but runtime spawning screws up the layer assignments your ground detection needs. Check your prefab’s layer settings and make sure the ground detection raycast uses the right layermask. My spawned characters kept ending up on the wrong layer, so the raycast couldn’t hit ground properly. Also make sure your NavMeshAgent’s enabled with a valid path before animations try to play walk cycles. Another gotcha - if you’re spawning on uneven terrain, characters need a frame or two to align with the NavMesh surface. The animation controller expects consistent ground contact, but spawned objects sometimes float above the walkable surface until the agent snaps to the mesh.
This sounds like a physics initialization problem. When you instantiate prefabs at runtime, collision detection needs time to register the new object. Your ground check probably fails because the character’s collider hasn’t been processed by the physics engine yet. I’ve hit this same issue. Call Physics.SyncTransforms() right after instantiation - it forces the physics system to update immediately. Without it, your raycast for ground detection hits empty space even though the character looks like it’s on the ground. Also check if your AI movement script starts before Awake() and Start() finish on all components. ThirdPersonCharacter might not be fully initialized when your AI logic kicks in. Try adding a one-frame delay with yield return null before enabling movement, or verify the animator component is ready before you modify applyRootMotion.
your navmesh agent probably isn’t synced with the animator. runtime spawning often breaks that connection. try manually setting the agent’s velocity in your animator parameters instead of letting it auto-detect. also check if your spawned prefab matches the editor version exactly - unity loves randomly resetting stuff during instantiation.
I’ve hit this timing issue tons of times. Your CheckGroundStatus method is probably running before the character controller or rigidbody has properly settled.
When you drop a prefab in the editor, Unity has all day to initialize everything in order. Runtime spawning? That’s when race conditions between systems bite you.
Add a small delay before the AI starts moving:
StartCoroutine(DelayedStart());
private IEnumerator DelayedStart() {
yield return new WaitForFixedUpdate();
yield return new WaitForFixedUpdate();
// Now start your AI logic
}
Also check if your ground detection raycast starts from the right spot. Spawned objects sometimes appear slightly above or below where they should.
About that applyRootMotion line - make sure you’re setting it at the right time. If the animator hasn’t fully loaded yet, changing root motion settings might not stick.