Can not delete skeletonMesh dynamic material(4.22.1)

I found an error in 4.22,my character in Seqeunce will automatically become a dynamic material,and it can’t be deleted.

I can delete them when the Sequence window opens,but when you open the Sequence again, it will still be created automatically.

When I exit the Sequece window at 4.21,Dynamic materials disappear automatically,so I think there is a problem with 4.22.

Hello,

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Thanks