I also saw this on Etho's channel. A minecart will go so far and freeze The chunk is there, the hitboxes are visible, but it appears invisible. You can dismount but the minecart is still stuck, but pushing it will let it go. Reloading the world or updating any blocks in the chunk will let the minecart go 16 more blocks, and then freeze. You now cannot get out. If you reload it will dismount you, and the chunk is fine. Happened to me dozens of times on my way to my Mesa Outpost.