Hello! Im not sure if this is a bug. However, when using a shield while wearing armor with Swift Sneak, you go the same speed as you are without the enchant.
Attached is a short demonstration of this "bug."
MC-249905
Snapshot 22w13a : Swift Sneak doesnt work with Shields
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I was unable to reproduce this. The speed was still slowed down but not to the effect without the Swift Sneak enchantment