Adding Entity to Track (Entity Is Already Tracked)

What the log looks like

net\.minecraft\.util\.ReportedException: Adding entity to track
"Silently" catching entity tracking error\.
java\.lang\.IllegalStateException: Entity is already tracked!

How to fix it

1. Read the stack trace directly below 'Adding entity to track' or 'spawnEntity' to check if a specific mod or plugin class is listed; if found, update or remove that mod/plugin.
2. If you are running SpongeForge or SpongeVanilla (indicated by 'org.spongepowered' in the log), update Sponge to the latest recommended build for your Minecraft version, as early beta builds had entity phase-tracking bugs.
3. If the error occurs whenever players enter a specific area (showing 'ChunkIOProvider' or 'loadChunk' in the trace), back up your world and enable 'removeErroringEntities' in forge.cfg (or forge-server.toml) to purge duplicate entities.
4. If corrupted chunk entities persist, open a backup of the world in an external NBT/region editor like MCA Selector and delete or reset the affected chunk where the log spam triggers.

Check your own log