@koyu2 Spinebot must have made up a skeletonRootMotion.Initialize() method, there is only SkeletonAnimation.Initialize(true).

What is the setup of your Rogidibody2D component?
You're assigning the Rigidbody2D to the property in the middle of the game. Does it work as expected if you set it before entering play-mode?

koyu2 Spinebot must have made up a skeletonRootMotion.Initialize() method, there is only SkeletonAnimation.Initialize(true)

Spinebotの情報は間違いだったのでしょうか？

Sorry to hear your problem persists! Yes, Spinebot was incorrect, there is no skeletonRootMotion.Initialize(true); method.

SkeletonDataAssetの再設定しつつ、rootmotionを再度有効にする方法はありますか？

It might have been translated incorrectly, but why reconfiguring SkeletonDataAsset?

In general the is nothing that needs to be done (like skeletonRootMotion.Initialize) after assigning an object at SkeletonRootMotion.rigidBody2D. If it does not work as desired even with setting update mode to FixedUpdate something else is going wrong. Could you please send us a minimal Unity project which still shows this issue? You can send it as a zip file to contact@esotericsoftware.com, briefly mentioning this forum thread URL so that we know the context. Then we can have a look at what's going wrong.

@koyu2 Oh, thanks for the clarification! I just noticed that the walk animation is not moving any bones at all and thus looked as if no animation at all was playing. I will investigade the cause of the problem.

@koyu Unfortunately the code is not minimal, the Character class which calls AnimationState.SetAnimation includes far too much functionality and seems to also call Rigidbody2D.AddForce if some conditions are met. Also there is an unnecessary SkinChanger component which seems to have nothing to do with the issue. Please note that we can't debug your character controller class.

Please create a minimal project where there is only a single script which sets your root-motion-walk animation without any input interaction. If the issue only arises when you add additional rigidbody interaction from code, add this code as well, but in as few lines as possible and without user input interaction. Please remove anything which can be removed.

@koyu2 Oh, I think now I understand your issue. Do you mean that you apply forces to your Rigidbody2D, but when you have the SkeletonRootMotion component set to target the Rigidbody2D, the forces you apply manually to the rigidbody no longer have any effect?

If so, likely your component is executed too early in the update cycle. FixedUpdate of your component shall be called after SkeletonRootMotion. You can set the script exectution order of your component higher e.g. by adding the line [DefaultExecutionOrder(2)] above your class.

An alternative would be to use skeletonRootMotion.AdditionalRigidbody2DMovement which is provided for such a reason:

/// <summary>Additional translation to add to <c>Rigidbody2D.MovePosition</c>
/// called in FixedUpdate. This can be necessary when multiple scripts call
/// <c>MovePosition</c>, where the last call overwrites the effect of preceding ones.

koyu2 [DefaultExecutionOrder(2)]

[DefaultExecutionOrder(2)] didn't have the desired effect of setting the script execution order to after SkeletonRootMotion because under Project Settings - Script Execution Order you have the script set to execution order -4. This obviously overrides the [DefaultExecutionOrder(2)] then.

koyu2 SkeletonRootMotionにRigidbody2Dを適用した途端、velocity_Yの数値がマイナス方向へ増え続けました。ジャンプするとvelocityに数値を代入しているので上空に飛びますが地面に着地後もvelocity_Yは減り続けています。

Unfortunately Rigidbody2D provides no grounded flag itself. As we can't determine safely whether your Rigidbody2D is grounded, you need to perform the test yourself, and then set applyRigidbody2DGravity accordingly.

You could write the test e.g. as follows:

protected bool isGrounded2D = false;

void OnCollisionStay2D (Collision2D collision) {
	foreach (ContactPoint2D contact in collision.contacts) {
		if (contact.normal.y > 0.5f) { // additionally you could check if the layer of the collision object whether it counts as a ground object, accessing contact.collider.gameObject.layer.
			isGrounded2D = true;
			return;
		}
	}
	isGrounded2D = false;
}

void OnCollisionExit2D (Collision2D collision) {
	isGrounded2D = false;
}

@koyu2 Sorry for the inconvenience! I just noticed that even when your Character script is executed after the SkeletonRootMotion component, adding a velocity vector to rigidbody2D.velocity does not have the desired effect. RigidBody2D.MovePosition() seems to not only set Rigidbody2D.velocity accordingly, but also zero any future modifications of Rigidbody2D.velocity after execution in the same frame.

There is a parameter skeletonRootMotionBase.AdditionalRigidbody2DMovement available, which can be used to set additional movement. Unfortunately it seems to be quite complicated to set persistent velocities. Nevertheless, the following code would be an adjusted equivalent of your script code using AdditionalRigidbody2DMovement:

public class Character : MonoBehaviour
{
    public Rigidbody2D chrRigid;
    protected SkeletonRootMotionBase rootMotion;

    protected void Awake()
    {
        chrRigid = GetComponent<Rigidbody2D>();
        rootMotion = GetComponent<SkeletonRootMotionBase>();
    }
    protected void FixedUpdate()
    {
		Vector2 additionalMovement = Vector2.zero;

		float input_X = Input.GetAxis("Horizontal");
		if (input_X != 0.0f) {
			additionalMovement.x = 10 * input_X * Time.deltaTime;
		}
		if (Input.GetKey(KeyCode.Space)) {
			additionalMovement.y = 30 * Time.deltaTime;
		}
		rootMotion.AdditionalRigidbody2DMovement = additionalMovement;
	}
}

The following component would then check for grounding, set rootMotion.applyRigidbody2DGravity = !isGrounded2D; and zero velocity upon grounding as well:

using UnityEngine;

public class ApplyGravityWhenGrounded : MonoBehaviour
{
	public bool isGrounded2D = false;
	protected SkeletonRootMotionBase rootMotion;
	protected new Rigidbody2D rigidbody2D;

	void Start () {
		rootMotion = this.GetComponent<SkeletonRootMotionBase>();
		rigidbody2D = this.GetComponent<Rigidbody2D>();
	}

	void OnCollisionStay2D (Collision2D collision) {
		foreach (ContactPoint2D contact in collision.contacts) {
			if (contact.normal.y > 0.5f) {
				isGrounded2D = true;
				rootMotion.applyRigidbody2DGravity = !isGrounded2D;
				rigidbody2D.velocity = new Vector2(rigidbody2D.velocity.x, 0f);
				return;
			}
		}
		isGrounded2D = false;
		rootMotion.applyRigidbody2DGravity = !isGrounded2D;
	}

	void OnCollisionExit2D (Collision2D collision) {
		isGrounded2D = false;
		rootMotion.applyRigidbody2DGravity = !isGrounded2D;
	}
}

We will investigate whether we can provide a better solution out of the box which makes adding forces and velocities easier.

@koyu2 FYI: While it is not a fix for more easily setting persistent velocities, we just fixed an issue with SkeletonRootMotion not updating it's references after changing SkeletonDataAsset and calling skeletonAnimation.Initialize(true). See this posting for details:
https://esotericsoftware.com/forum/d/26488-游戏运行中是否可以切换skeletondataasset/3

We will let you know once we have an improvement to offer for setting velocities.