The shield in the offhand disappears when the game is paused. When the shield is on the main hand, it instead appears differently than what should it appear as. If it's in third person mode, the shield appears on top of the player's shoulder. This bug does not happen when the Game Pause option in the settings is off.
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We're tracking this issue in MCPE-190218, so this ticket is being resolved and linked as a duplicate.
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