If you're swiming while in elytra mode the elytra looses durability even tho you're swiming. to stop elytra mode you need to stand on a block.
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Avoma
Hey there!
This appears to be a duplicate of MC-97190 which was later marked as "Works As Intended", so this issue you are experiencing here isn't actually a bug. I hope this helps clear any confusion and Merry Christmas!