The s pen does have a small amount of play, but that's just the part that clicks. If the s pen itself slips/slides out of the slot when shaking the device in a up and down fashion, I would have to guess that the mechanism that locks the tip of the s pen into the device is loose and broken. Or maybe just the part on the end of the s pen that clicks up and down broke? Either way, I reckon you reach out to Samsung or even your phone carrier to get that resolved.
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