Although labelled as waterproof, if you read the small print, it says in fresh water only, in a swimming pool it has chlorine in it, so therefore not classed as fresh water which means you shouldn't use the phone there. Stupid I know, but this could be your issue. I ran my phone under a running tap for 20 seconds and after that the speaker was distorted and the touchscreen was not working right. After leaving it to dry for a short time, I turned it back on and it worked fine, I wouldn't do it again, I don't trust it!
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