When user joins a realm as a split screen player (user has been previously invited and added to the realm), they are added under their name, but as what appears to be a guest character, often beginning at spawn. They have no inventory. In other words, although they are properly logged in, and their name appears associated with the character, the character is not them but a guest.
We're tracking this issue at MCPE-233088, so I will resolve and link this report as a duplicate.
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