Modded Multiplayer — Compatibility & Troubleshooting

Most “my friend can’t connect with mods on” reports in 1.0 come down to one of three causes, in this order: crossplay is on, a client is missing a mod the server runs, or a mod’s version has drifted after a patch. Work through them in that order — the crossplay block is by far the most common and the only one with no workaround.

Honesty note (what we have and have not verified): the causes below are stable and well established (the crossplay block is architectural, the desync is a known behaviour). We have not, however, published a tested, reproducible “mod X breaks connection” list for 1.0, because the specific set of broken mods shifts in the days after each patch. Use the checklist as a diagnosis method, not a definitive bug list.

1. Crossplay is on — the hard block

This is the one with no workaround. BepInEx hooks the Steam networking path; with crossplay enabled Valheim uses PlayFab instead, so a modded PC session cannot be joined by crossplay clients. Symptom: the modded host sees no one connect, and crossplay friends see nothing at all.

Fix: decide the group’s platform makeup first.

• All Steam, no console: every PC player disables crossplay in settings, the host drops the -crossplay flag (dedicated server), and everyone uses mods freely.
• Any console player in the group: keep crossplay on and run vanilla. You cannot mix — see crossplay for the mechanics.

2. A client is missing a mod the server runs (desync)

For mods that are server-side or both, every joining client must run the same mod at the same version. If one player has a combat, loot, or crafting mod the others lack, the world state diverges and you get desync, stuck items, or failed joins.

Fix: before anyone joins, make sure the mod set is identical on the server and every client — same mods, same versions. Check each mod’s Thunderstore page for its Side field (Client, Server, or Both) to know who actually needs it. The full breakdown is in server-side vs client-side mods.

Client-only mods (cosmetics, UI, minimap) are the easy case: only the player who wants them installs them; the server and others do not.

3. A mod drifted after a patch

Every major Valheim update breaks some mods temporarily, and 1.0 was a bigger-than-usual update (engine upgrade + new biome + new networking layer). A mod that worked last week may be mid-update now. The usual pattern: quality-of-life mods update first, bigger combat/loot overhauls take longer, and anything touching networking or low-level systems lags furthest behind.

Fix: check each mod’s page for a 1.0 / Deep North compatible version, or pin a version you know is stable. The state of the ecosystem in more depth is in the post-1.0 mod scene.

The quick checklist

1. How many console players are in the group? If any — vanilla only, stop here.
2. Is the mod set identical on the server and every client (same mods, same versions)?
3. Does every mod you run show as 1.0 / Deep North compatible right now?
4. Did a patch land recently? Re-check the mods that touch combat, loot, or networking.

If all four are yes and it still fails, the remaining case is a genuinely broken mod or a save-specific issue — the best next step is to test on a copy of your world rather than your main save, so a failing mod cannot corrupt it.

Links

• crossplay — the networking mechanics behind the hard block
• server-vs-client-mods — who has to install what
• dedicated-server-guide — setting up the server and the -crossplay flag
• mod-ecosystem-1-0 — what has and has not adapted
• bepinex-setup — the loader everything above depends on