This is something that has happened to youtuber doctor nok and in his video he showed that his character disappeared under water, he was in the 20w06a. He starts talking about it from second 25
link of the video: https://youtu.be/nxuD3yq3Hzo
(i cant put the video downloaded because its too big and i cant compress it)
Duplicate of MC-197328. (just to let you know, there is a typo in the description, you typed "20w06a" instead of "21w06a")