I was playing Minecraft 1.16.5 on a Realm with my friend, and I had caught a llama with a lead. I had a door in my hand, and as I tried to leash the llama to a fence the lead appeared on the fence and half of the door above it. I laughed over the half-door and then tried to open it, and the door disappeared. A second lead then dropped onto the ground and I picked it up. Every time I moved the new lead into my hotbar, another lead appeared. I accumulated 5 before they all disappeared, the door was returned to me, and everything was fine. Not a dangerous issue, but odd nonetheless.
Part 1: https://www.twitch.tv/fryguythe777th/clip/EndearingTenderPoultryPJSalt-4bDTzHJYScJ7QQU
Part 2: https://www.twitch.tv/fryguythe777th/clip/DifficultSplendidHamBloodTrail-p5lvZz1K_e7Na3fa
This issue is already being tracked at MC-158774.
This is a client-server desync, which causes many strange, but temporary, issues like the ones you experienced.