I was working on a game of mine, when all of the sudden the world was hit with extreme amounts of lag. My camera was jittery, mobs were slowed and buggy, and was overall very laggy. I started a new world think it would fix the issue, and was wrong. On a brand new flat world with no experimental features, addons, or texture packs, I still got the extreme lag. When I exit the world, the lag is so bad it causes the world size to go from around 15 megabytes to around 250-300! Keep in mind that the worlds I am referring to are brand new flat worlds, with NO experimental features OR addons/textures of any kind. This bug is catastrophic, and must be fixed! For a cause, it is unknown. I will spawn in, make a flying platform with a fill command that consists of around 4000 blocks, and my game starts lagging very bad. I will turn off command blocks and kill all entities, and the lag still persists. I have made 3 brand new flat worlds, and am still having the same issue. This is NOT a hardware issue, because the lag is in the entities and blocks being delayed, rather than frame drops or something like that. Doing something in the game like this used to work fine, meaning this is entirely the games fault. I have minimal settings on, and have done many things on my end to try to resolve the issue. There is literally no more evidence I can give you, as this description says it all. I understand that lag is a broad topic that happens especially when there is lots of players in worlds or big worlds or something like that, that you get a lot of useless reports from, but it is EXTREMELY alarming when there is no cause for the lag. I have tested a variety of things to see if they cause the lag such as ticking areas, fill commands, and completely turning off commands. Also, all of these flat worlds are solo, no experiments, all vanilla, no addons/textures.