Default USB cover distorted

The USB cover on my lovely phone has become distorted for no good reason. I hardly ever remove it because I use magnetic chargers so I have no idea how it happened.
It is distorted at both ends so that, when you rub a finger across it, the ends are raised up.
I hope the waterproofing is not affected.
Anyone else seen this issue and have any idea how it occurred.
See the attached image.
Attached Thumbnails
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