the shield disappears when held in the left hand

when I play survival, I make a Shield for protection when I explore a cave that has a lot of monsters. Because, my right hand holds a sword. So, I held the "Shield" in my left hand. When I continued exploring the cave, I thought "Where did the shield I hold in my left hand go, how come it disappeared". When I opened the inventory, the Shield was still there. I tried to squat, it turns out the Shield is there. However, when I walk/run the Shield isn't even there