Minecraft Bedrock v1.16 on Ubuntu Server 18.04 LTS VM on Hyper-V Server. Dual Xeon E5-2667v2 (4GHz max frequency), Intel S2600CO4, 256GB registered ECC RAM, dual Intel 750 NVMe SSDs.

Lag hasn't been great on this world for a while, particularly around the home base that has a few dozen villagers, extensive mines, lots of torches etc. However, after the Nether Update (v1.16) dropped this week (the server auto-updates and runs a backup every morning at 4am) this world/server is basically unplayable in the Overworld (if you can make it to the Nether, that seems to work fine). Clearly a world that's been played in for a year or so is going to have quite a lot of changes, but the result is that it takes about twenty minutes to load in the world (everything's transparent and you can't move the character until then), and then everything is very laggy and stuttery. Shooting a box causes the arrow to drop out of the sky about halfway to the target, mobs move like a 1 frame per three second slideshow. Giving the server a whole hour to load the world doesn't help - the immediate environment may render, but as soon as you start moving around you can quickly find areas with no textures loaded (and that's just running - flying is impossible as you hit invisible walls almost immediately).

To investigate this, I've tried numerous things. First I added extra CPU cores and memory (usually has 4 cores and 8GB RAM allocated), increasing the CPU and memory weight so the Hyper-V server prioritises this VM over everything else (8 CPU cores and 64GB of RAM allocated). Memory usage typically only hits 2 or 3GB, but I wanted to see what would happen if I gave it everything I could - it made no difference. Whatever the limitation is with a Minecraft server, it isn't performance of the underlying hardware.

I went into the world and used the /kill command to kill everything, logged out and back in, it made no difference.

So I'm at a loss here - my son spent all week bouncing off the walls waiting to play the new Nether update, only to have his expectations dashed with a game that's utterly unplayable. He's had to satisfy himself with playing local worlds generated on the PC.

Why has the 1.16 update caused such catastrophic performance issues? He's been building in that world for ages, there's no way we're just going to abandon it and start again. But we're stuck between a rock and a hard place, because it is completely, totally unplayable in its current state.