After having trimmed armor in a lot in your creative inventory and then removing said armor from your creative inventory. Any armor placed in the same slots the previous trimmed armor was placed in will render those same trims on new, untrimmed armor. Issue is fixed when world is restarted.

Steps to recreate:

1. Load up Minecraft Bedrock Edition 1.21.51
2. Make a creative world
3. Put a piece of trimmed armor in your inventory
4. Remove that piece of trimmed armor from your inventory
5. Place new, untrimmed armor into same slots as trimmed armor previously was