DEUF - Duplicate Entity UUID Fix [NeoForge]

Changes UUIDs of loaded Entities in case their UUIDs are already assigned (and removes log spam).

872 Downloads

neoforgecursedoptimizationutility

Rent Server with this Mod

About this Mod

"Keeping entity minecraft:xxxx that already exists with UUID xxxx"

Now that message can occur quite often in case you use an old world. And there is no fix for it currently even though the bug is listed in the bug tracker for some time now. The logs (and server console, in case you have one - like me) also get spammed quite a lot so I thought I would make a mod which fixes those duplicate UUIDs and thus removes the spam.

Simply drag and drop the file into your mods folder. Clients do not need to install the mod to join your server (in case you use it for a server - like I do).

When installed, simply explore your world. Initially the spam will be more than before, since there should be an additional message which tells you that the UUID has been changed. But when reloading the world or restarting the server, that will not occur anymore for that exact entity, which now has a non-duplicate UUID.

Port of CAS_ual_TY's DEUF to NeoForge 1.21.1+ under the MIT license.

Available Versions

DEUF - Duplicate Entity UUID Fix [NeoForge] 26.1-1.0release

MC 26.1neoforge

March 24, 2026

DEUF - Duplicate Entity UUID Fix [NeoForge] 1.21.1-1.0release

MC 1.21.1, 1.21.2, 1.21.3, 1.21.4, 1.21.5, 1.21.6, 1.21.7, 1.21.8, 1.21.9, 1.21.10, 1.21.11neoforge

March 5, 2026

How to Install DEUF - Duplicate Entity UUID Fix [NeoForge] on Your Server

Order Server

Order a Minecraft Java server with at least 3 GB RAM (4 GB recommended).

Set neoforge Loader

In the panel under "Egg", select the neoforge loader and matching Minecraft version (26.1).

Install Mod

Open the mod browser in the dashboard and search for "DEUF - Duplicate Entity UUID Fix [NeoForge]". Click "Install" – done! Alternatively, upload the .jar via SFTP to the /mods folder.

Compatibility

Mod Loaders

neoforge

Minecraft Versions

26.1, 1.21.11, 1.21.10 (+9 more)

Server-side

✓ Required

Recommended RAM

4 GB(min. 3 GB)

Frequently Asked Questions

DEUF - Duplicate Entity UUID Fix [NeoForge] server crashes on startup – what to do?

Most common cause: wrong neoforge version or insufficient RAM. Check the server log (latest.log) for "OutOfMemoryError" or "Mixin" errors. With Mado Hosting: ensure at least 3 GB RAM is allocated and the loader matches the mod version (26.1). You can switch loaders with one click in the panel.

Is DEUF - Duplicate Entity UUID Fix [NeoForge] compatible with neoforge?

DEUF - Duplicate Entity UUID Fix [NeoForge] officially supports neoforge for Minecraft 26.1, 1.21.11, 1.21.10. The Mado dashboard automatically detects incompatible loader combinations.

Server lagging with DEUF - Duplicate Entity UUID Fix [NeoForge] – how to optimize performance?

Recommended RAM: 4 GB (per 8 players). Use /spark profiler to check if DEUF - Duplicate Entity UUID Fix [NeoForge] consumes the most tick time. Common fixes: reduce server view-distance to 8-10, install "performant" or "starlight" as supplementary mods on Forge. With Mado Hosting, your server runs on NVMe SSDs with dedicated CPU cores for minimal latency.