Why is iPhone XS Max suddenly losing sounds while in sleep mode?

It occurs about 3 times a week. More frequently when the iphone is in airplane mode or the Wi-Fi is off. I have tried resetting all configurations and deleting, restarting with iTunes, updating but the issue reappears. I took it to the authorized Apple technical service in Colombia, but they didn't find any problem. Has anyone else had this problem or knows about it? What can I do?

The factory warranty on the phone will expire soon. Keep taking it back until they swap it out for a new one. You may need to call the Apple support number.

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