Even if set to left handed, the (empty) right hand is visible for a short time in the lower middle of the screen after joining a world (e.g. opening in Singleplayer) before the hands update to being in the correct position and holding the correct items.
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Comments 11
Either my previous comment was wrong or it has changed back. It shows the hand on the right for a single frame now.
Can confirm in 1.13.1