java.lang.IllegalStateException: Not building! (BufferBuilder Render Crash)

What the log looks like

java\.lang\.IllegalStateException: Not building!
at net\.minecraft\.client\.render(?:er)?\.BufferBuilder\.(?:ensureBuilding|func_178977_d)\(

How to fix it

1. If you are using Iris Shaders with Sodium (or Oculus with Embeddium/Rubidium), update both mods to the latest matching versions for your Minecraft release, as mismatched versions break batched entity rendering.
2. Remove Not Enough Crashes (or similar crash-catching mods) if installed, then reproduce the crash so you can see the original error instead of a corrupted render state.
3. Look at the crash report stack trace right below the `BufferBuilder` and `Tessellator` lines to find the mod package triggering the bad draw call (for example, `com.vicmatskiv.weaponlib` points to Vic's Modern Warfare).
4. Update or remove the mod identified in the stack trace, or test without OptiFine/shaders enabled if the crash happens when holding or viewing a modded 3D item.

Check your own log