Factorio Desync Fix: Why Multiplayer Desyncs and How to Stop It

A Factorio desync means your game and the server stopped simulating the map identically, so the client disconnects you and builds a desync report. Desyncs are bugs, almost always in a mod or scenario, sometimes in Factorio itself or faulty hardware. Lag and bad internet do not cause them. Restarting the server usually gets everyone back in short term.

What is a desync in Factorio?

Factorio multiplayer uses deterministic lockstep. Instead of sending the whole map over the network, the server only shares player inputs, and every player's computer simulates every tick of the entire map itself. That is why huge factories work in multiplayer at all. The catch is that every machine must reach exactly the same result every tick. When one player's game calculates anything even slightly differently, the states no longer agree. That disagreement is a desync.

The official Factorio wiki on desynchronization is blunt about the causes: "a bug in Factorio code, a bug in a mod/scenario, a miscalculation on server or client hardware". It also states that "Networking-, latency or performance problems do not cause desyncs."

What happens when you desync?

When your client detects a desync it disconnects you, downloads the server's map and game state, and generates a desync report. That download takes longer than a normal join. Afterwards you get three choices: view the report, quit, or reconnect.

The report contains:

Because it holds two full saves with extra debug data, a desync report can be large. It does not say what caused the desync. It is a snapshot for modders and Wube to investigate.

Quick fix: get everyone playing again

1. Click Reconnect. A one off desync often does not come back.
2. If it repeats, restart the server. A restart reloads the map cleanly and usually lets everyone rejoin until whatever triggered the bug happens again.
3. Make sure everyone is on the exact same version as the server. A version difference normally blocks the join outright, but players who switched branches on Steam should check. See the Factorio version mismatch fix.
4. Make sure every player's mods match the server. Accept the mod sync prompt when joining rather than installing mods by hand.

If the same player desyncs again within minutes of reconnecting, move on to finding the cause.

How do you find which mod causes a desync?

Most desyncs in modded games come from a mod. The wiki suggests this order:

1. Note what was happening. Was it a train arriving, a player opening a certain GUI, a research finishing, a specific time? Desyncs are usually tied to an activity.
2. Roll back recently added or updated mods. If the desyncs started after you added or updated a mod, that mod is the top suspect. Factorio lets you pick older mod releases on the mod portal.
3. Remove mods on a test copy of the save. Never test on your only copy. Make a backup, then remove mods in halves until the desync stops.
4. Re add the suspect and reproduce it. Once you can trigger the desync with one mod enabled and not without it, you have the cause.
5. Report it to the mod author with the desync report and a description of the activity. Mod pages on mods.factorio.com have a discussion tab for bug reports.

If you know some Lua, the console command /toggle-heavy-mode makes Factorio save and reload every tick and flags state changes, writing dumps to a dumps folder in your user data folder. It is slow and meant for testing on a copy, not for normal play.

What if there are no mods?

A desync with zero mods and no custom scenario is a bug in Factorio itself or a hardware fault. Post the desync report and what was happening in the Factorio bug reports forum. Wube fixes desyncs regularly: the 2.0.77 release, stable since 23 June 2026, for example lists "Fixed a desync related to custom input events and in_gui flag" (2.0.77 changelog). Staying on the newest version helps.

If only one player ever desyncs, and always at random, their hardware is worth checking. Unstable RAM or an overclocked CPU can produce calculation errors that look exactly like a desync. Running a memory test and removing any overclock is a sensible step.

Desyncs on Factorio 2.1 experimental

Factorio 2.1 has been on the experimental branch since June 2026, and experimental builds plus freshly updated mods are where new desyncs tend to appear. If your group moved to 2.1 and desyncs started, consider going back to stable 2.0.77 from a backup made before the switch, since 2.1 saves cannot be downgraded. More in our Factorio 2.1 update guide.

Desync vs lag vs mod mismatch

These problems get mixed up, but each has a different fix:

Slowdown in a big factory is a UPS problem, not a desync. Since every player simulates the whole map, the slowest computer sets the pace for everyone.

Fixing desyncs on a GamezServers Factorio server

On our servers you can do every step above from the panel:

• Restart the server from the dashboard to clear a desync loop.
• Back up before testing mods, then restore if a test goes wrong.
• Edit mods in the mods folder from the Files tab and turn them on or off in mod-list.json. The mod installation guide shows the format.
• Pin a version with the Factorio version setting if a new release introduces problems.

Plans start at 4.99 USD a month for 2 GB. See Factorio server hosting.

FAQ

Does lag cause desyncs in Factorio?

No. Factorio's own documentation states that networking, latency and performance problems do not cause desyncs. Lag causes slowdown or stutter, not a desync report.

Why do I keep desyncing on a modded Factorio server?

Usually a mod has a bug that makes its behaviour differ between players. Roll back recently updated mods, then remove mods on a test copy until it stops, and report the culprit to its author.

Where is the Factorio desync report?

After a desync, use the view report option on the disconnect screen to open it. It is stored in your Factorio user data folder, which on Windows is %appdata%\Factorio.

Will restarting the server fix a desync?

Often, in the short term. A restart reloads a clean state, but the desync can return when the same bug is triggered again.

Can one player's PC cause desyncs?

Yes. Faulty RAM or an unstable overclock can make one machine calculate differently. If only one player desyncs, check their hardware.