Upgrading my Minecraft Create World from Forge 1.20.1 to NeoForge 1.21.1

The Great Migration to Minecraft 1.21.1 – Was It Worth It?

After spending countless hours building and expanding my Create Mod world, I finally made the decision to migrate everything from Minecraft 1.20.1 Forge to Minecraft 1.21.1 NeoForge. This wasn't a decision I made lightly, as my world has grown into a massive project with a large railway network, factories, roads, MineColonies, custom infrastructure and many Create Mod add-ons.

So why risk everything?

The answer is simple: Create: Coasters Simulated.

This amazing mod is currently only available for Minecraft 1.21.1, and I have been planning to build a huge amusement park inside my Create world for quite some time. Roller coasters, dark rides and realistic attractions have always been part of my long-term vision, and this mod finally makes that possible. 

Preparing for the Upgrade

Before updating, I created several backups of my entire world. Even though I was confident that everything would work, migrating a large modded world is never without risk.

This wasn't just a Minecraft update. The migration included:

  • Forge → NeoForge
  • Minecraft 1.20.1 → 1.21.1
  • Updated versions of Create and many other mods
  • Internal changes to world data and mod systems

Fortunately, I later discovered that the Forge to NeoForge migration itself worked perfectly. The real problems only started after updating the world to Minecraft 1.21.1.

The First Signs of Trouble

As soon as I loaded the updated world, I immediately noticed that something wasn't right.

The world itself loaded successfully. Buildings were still there, machines existed, trains could move and nothing had completely disappeared.

Unfortunately, several Create-related systems had been damaged during the migration. 

Missing Railway Tracks

The first issue appeared throughout my railway network.

Random railway track pieces were simply invisible.

At first I thought the tracks had been deleted, but after some testing I discovered something very strange:

  • Trains could still drive over the invisible tracks.
  • The railway network was still fully connected.
  • Wheel particles appeared normally.
  • Breaking the invisible tracks dropped the correct track items.

This meant the tracks still existed internally—the game simply failed to render parts of them correctly.

Even more interesting, this affected both normal Create tracks and Steam 'n' Rails tracks, making it clear that the issue was related to Create's railway system itself.

Broken Railway Signals

The next major problem involved railway signals.

Some signals became invisible while still blocking railway sections internally.

Even after removing a signal, the reserved track section often remained blocked.

The only reliable solution was:

  1. Remove the affected track.
  2. Remove the invisible signal.
  3. Place the track again.
  4. Create a completely new signal.

Considering the size of my railway network, this turned into many hours of manual repair work.

Every Create Filter Was Empty

Another unexpected problem affected every Create filter inside my factories.

All configured filter lists had completely disappeared.

The machines themselves were still present and working, but every single filter had to be configured again manually.

For a world with dozens of automated production lines, this became another large repair project.

MineColonies Nearly Gave Me a Heart Attack

At first it looked like my entire MineColonies colony had been destroyed.

The buildings were still standing, but every citizen had disappeared.

After investigating the world files, I discovered that the colonies.dat file had been replaced during the migration.

Luckily, I still had the original file from my backup.

After manually restoring it, every citizen immediately returned and the colony started working again.

That was definitely one of the biggest reliefs during the entire migration.

Hours of Testing

I spent many hours trying to understand what had actually happened.

Among other things, I tested:

  • Different Create versions.
  • Different NeoForge versions.
  • The unofficial Steam 'n' Rails port.
  • Replacing Create track data files.
  • Comparing old and new world files.
  • Migrating the world step by step.

The most important discovery came after performing the migration in two stages.

First, I migrated the world from Forge 1.20.1 to NeoForge 1.20.1.

Everything worked perfectly.

Only after updating the exact same world from NeoForge 1.20.1 to NeoForge 1.21.1 did all Create-related issues appear again.

That confirmed the world itself was not corrupted—the problems were introduced during the Minecraft 1.21.1 migration.

Repairing Everything Manually

Since there was no automatic fix available, I decided to repair everything by hand.

This included:

  • Replacing invisible railway tracks.
  • Rebuilding broken railway signals.
  • Restoring every Create filter list.
  • Testing the complete railway network.
  • Verifying every major factory still worked correctly.

It certainly took a lot of time, but in the end the effort was worth it.

Looking Ahead

Now that the migration has finally been completed and all major systems have been repaired, I can finally focus on the reason why I upgraded in the first place.

The next major project for this world will be a fully functional amusement park built with Create: Coasters Simulated.

I already have plenty of ideas for roller coasters, transportation rides, themed attractions and realistic stations that will connect with my existing railway network.

This will become one of the biggest projects I have ever built inside Minecraft. 

Final Thoughts

Looking back, the migration was definitely more difficult than I expected.

There were moments when I honestly thought the world might be permanently damaged.

Fortunately, that wasn't the case.

Almost everything could be repaired manually, and today the world is fully playable again.

Considering the size and complexity of this project, I actually feel very lucky. A migration of this scale could easily have resulted in corrupted chunks, missing structures or even a world that refused to load at all.

Instead, I "only" had to repair railway tracks, railway signals and Create filter lists.

While it required many hours of work, it was a small price to pay for unlocking everything Minecraft 1.21.1 has to offer.

The future of this world is now even more exciting than before—and the construction of my dream amusement park can finally begin.

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