Setting AnimationMode to "UseAnimationAsset" inside Sequencer might not be set properly.

Adding a new key inside a LevelSequence that changes the AnimationMode of a SkeletalMesh to "Use Animation Asset" can bug out the AnimationMode constantly change between "UseCustomMode" and "UseAnimationAsset".

This makes that the character keeps switching between T-Pose and the selected Animation. After some debugging, it looks like the issue is triggered more easily if the sequencer has a lot of tracks in it. This bug was not happening in version 5.2. It might be caused by the introduction of MovieSceneTaskSceduler.

• With the user repro case:

1- Open the LevelSequencer that the user created.
2- Reproduce in loop the sequence. You will see in the BP_ThirdPersonCharacter details pannel that when the "Use Animation Asset" key is reached, the AnimationMode will be changing intermittently between "UseAnimationAsset" and "Use Custom Mode".

• Without repro case:

1- Open a new Unreal Engine 5.4.4 project from the ThirdPersonTemplate.
2- Create a LevelSequence. Add the BP_ThirdPersonCharacter as a spawnable as a Sequencer track.
3- From the CharacterMesh of the Blueprint, Add an AnimationTrack. Create two keyframes. At frame 0 with Use AnimationBlueprint, and after some frames, a new keyframe with UseAnimationAsset.
4- Spawn 50 lights in the scene and add them in the sequencer. This issue happens more often when the sequencer has a lot of tracks.
5- From the CharacterMesh, spawn a AnimationTrack with the MF_RunFwd animation. The animation should start at the same frame as "Use Animation Asset" key.

• With the user ReproCase:

1- Open the LevelSequencer that the user created.
2- Reproduce in loop the sequence. You will see in the BP_ThirdPersonCharacter details panel that when the "Use Animation Asset" key is reached, the AnimationMode will be changing intermittently between "UseAnimationAsset" and "Use Custom Mode".

• Without repro case:

1- Open a new Unreal Engine 5.4.4 project from the ThirdPersonTemplate.
2- Create a LevelSequence. Add the BP_ThirdPersonCharacter as a spawnable as a Sequencer track.
3- From the CharacterMesh of the Blueprint, add an AnimationTrack. Create two key frames. At frame 0 with Use AnimationBlueprint, and after some frames, a new key frame with UseAnimationAsset.
4- Spawn 50 lights in the scene and add them in the sequencer. This issue happens more often when the sequencer has a lot of tracks.
5- From the CharacterMesh, spawn a AnimationTrack with the MF_RunFwd animation. The animation should start at the same frame as "Use Animation Asset" key.
6- Reproduce in loop the sequence. You will see in the BP_ThirdPersonCharacter details panel that when the "Use Animation Asset" key is reached, the AnimationMode will be changing intermittently between "UseAnimationAsset" and "Use Custom Mode".