The 1.0 update landed on 9 September 2026 and, within hours, the most common Valheim server problem on the internet became a single sentence: "my server won't start since the update." Almost every one of those servers has one thing in common — a mod loader. Here is why 1.0 broke modded servers, how to get yours booting again in five minutes, and how to run mods afterwards without repeating the outage.
Why 1.0 broke mods
Valheim has no official mod support and no Steam Workshop. Every mod runs through BepInEx, a loader that hooks into the game's code at start-up, and the mods themselves patch specific functions inside the game. When Iron Gate changes those functions — and 1.0 changed a great deal, from a new biome to a new world version — the patches point at code that has moved or no longer exists.
Two things then happen:
- Mods written against pre-1.0 code throw errors or silently do nothing.
- BepInEx and the loader plugins themselves may need a new build for the updated game, and until that build exists, the loader can stop the server from starting at all.
Iron Gate said before launch that they could not guarantee existing mods would work after 1.0 and that there was no early build for mod authors to test against. That warning was accurate.
What the crash actually looks like (we reproduced it)
We took a 1.0 server, enabled the BepInEx loader that shipped with the pre-1.0 Valheim Plus package, and started it with crossplay on. It never reached the world. The console ends like this, then the server restarts and does it again:
cant resolve internal call to "System.MissingMemberException::FormatSignature"
Your mono runtime and class libraries are out of sync.
The out of sync library is: /home/container/unstripped_corlib/mscorlib.dll
...
#19 0x000000404cb203 in BepInEx.Preloader.Entrypoint:Main ()
Detected server process in a crashed state!
The reason is in the 1.0 patch notes: Iron Gate upgraded the Unity engine. A BepInEx pack carries its own copy of the Mono class libraries (unstripped_corlib), matched to the engine it was built for. The new engine rejects the old copy before a single mod loads — so the crash happens even with an empty plugins folder. Only a loader build made for the 1.0 engine can get past that line.
The fast fix: boot vanilla first
Get the server running without any mods, confirm the world loads, then reintroduce mods one at a time. On a self-hosted server:
- Stop the server.
- Back up the world —
<World>.db and <World>.fwl from your save directory — before touching anything.
- Rename the
BepInEx folder to BepInEx.off (or move it out of the server directory entirely). Do the same for doorstop_libs, unstripped_corlib, doorstop_config.ini, winhttp.dll and libdoorstop_x64.so if present.
- Make sure you're starting the server with the vanilla launch line, not
start_server_bepinex.sh.
- Start. Watch for
Load world: and, on a crossplay server, registered with join code.
If that boots, the game and your world are fine and the problem is entirely the mod stack. If it still doesn't boot, the mods were never the problem — check the dedicated server guide for the password rules that stop a server silently.
Reintroducing mods after 1.0
- Update the loader first. Get the current BepInEx build for Valheim from its Thunderstore or GitHub page and check that its release notes mention 1.0 compatibility. An old loader with new mods is as broken as the reverse.
- Read each mod's page before re-enabling it. Authors post "updated for 1.0" notes; mods with no update since launch are suspect.
- One mod per restart. Enable, boot, check the console for red errors, join, play for five minutes. Then the next one. Adding twenty at once and bisecting afterwards costs an evening.
- Server and client versions must match. Most gameplay mods must be installed on every player's PC too, at the same version as the server. A player with an older copy of a mod gets kicked or desynced.
- Console players can't have mods. A modded server is effectively PC-only. If the point of 1.0 for your group was getting PS5 and Switch 2 friends in (how crossplay joins work), stay vanilla.
Mods that touch the world are the dangerous ones
Cosmetic and quality-of-life mods fail safe: remove them and nothing is lost. Mods that add items, buildings or biomes write into the save. Remove one of those after a world has used it and the objects it created become missing pieces — sometimes harmless, sometimes a crash on load. That is exactly why the backup in step 2 above is not optional, and why the RAM guide budgets extra memory for modded worlds.
Every future patch is a smaller version of today
1.0 is not the last update. Each patch can break the loader or individual mods again, and if your server updates automatically on restart — which it should, or players can't join — a modded server can go down at 4am after a scheduled restart. Habits that keep a modded server sane:
- Watch the console after any restart that followed a Steam update.
- Keep the vanilla launch line ready so you can boot without mods in one step.
- Turn off automatic updates only while you're actively waiting for mod authors, then turn them back on.
Frequently Asked Questions
Does Valheim 1.0 support mods?
There is still no official mod support and no Steam Workshop. Mods use BepInEx, and Iron Gate has said they can't guarantee mods work after 1.0.
Will my mods work after the update?
Some will after their authors update them; many did not on launch day. Boot vanilla first, then re-enable updated mods one by one.
Can console players join a modded server?
No. Mods can't be installed on PlayStation, Xbox or Switch 2, so a modded server is effectively PC-only.
Do hosts support mods?
Most hosts, Connect included, run the official vanilla server and give you file access for BepInEx at your own risk. Nobody can promise a third-party loader survives Iron Gate's patches.
If you'd rather never debug a loader at 4am: Connect Valheim servers run the official 1.0 server, update themselves on restart, and keep backups you can roll back to — with full file access if you still want to experiment.