I was playing Minecraft for Nintendo Switch when I encountered a bug (as shown in the video.) I managed to replicate the bug many times and captured the bug in the clip below.
I tried to recreate the bug by being signed into my Microsoft Account on one attempt, then I tried using only my Nintendo Account and finally, I tried disconnecting my Switch from the internet and I got the bug every time I opened up the world, connected to the internet or not.

P.S. I never tried to recreate the bug on Xbox One or iOS because the world was saved to my Switch, not my Realm.

P.P.S I opened the world on my iPad Air (old iPad. I know) using my realm, and the bug never occurred.