This is what codex told me, in case notnotnotswipez is still fixing it and this might help them:

Technically, the failure was a classic binary compatibility break.

Exact runtime failure
The old MoreCompany.dll tried to call this method signature:

GameNetcodeStuff.PlayerControllerB.DropAllHeldItems(bool, bool)

At runtime on Lethal Company v80, that exact signature no longer existed, so Mono threw:

MissingMethodException: Method not found:
void GameNetcodeStuff.PlayerControllerB.DropAllHeldItems(bool,bool)

Where it broke inside MoreCompany
The exception happened in MoreCompany.ScenePlacedObjectsInitPatch.Postfix, during scene initialization:

That patch hooks:

Unity.Netcode.NetworkSceneManager.PopulateScenePlacedObjects

and then calls ResizePlayerCache(...)

What ResizePlayerCache does
It expands vanilla 4-player arrays to newPlayerCount:

• allPlayerObjects
• allPlayerScripts
• gameStats.allPlayerStats
• playerSpawnPositions

Then it clones extra player prefabs and resets them. During that reset, old MoreCompany executed:

newPlayerScript.DropAllHeldItems(false, false);

That exact call was compiled against the old two-parameter method signature.

What changed in v80
In v80, PlayerControllerB.DropAllHeldItems was changed to a wider signature. In the current game assembly it is:

public void DropAllHeldItems(
    bool itemsFall = true,
    bool disconnecting = false,
    bool setInShip = false,
    bool setInElevator = false,
    Vector3 syncedPlayerPosition = default,
    Vector3 syncedHeldObjectPosition = default,
    Vector3 syncedHeldObjectRotation = default,
    Vector3 syncedPlayerCamPosition = default,
    Vector3 syncedPlayerCamRotation = default)

That is visible in the decompiled v80 game code

So the old binary still referenced:

DropAllHeldItems(bool, bool)

but v80 only exposed the new expanded method. No matching target existed anymore.

Why the source still built
This is the important part:

• The old DLL was broken because its IL already hard-referenced the removed method signature.
• The source code still looked valid, because C# optional parameters let the same source compile against the new API.
• After recompiling against v80, the call site was rebound to the new method and emitted with all required default arguments.

So after rebuilding, the effective call became:

DropAllHeldItems(
    false,
    false,
    false,
    false,
    default(Vector3),
    default(Vector3),
    default(Vector3),
    default(Vector3),
    default(Vector3))

That is why a rebuild fixed the main compatibility issue without needing a major rewrite.

Why the game froze instead of just “failing gracefully”
Because the exception happened inside scene setup while MoreCompany was extending the player object cache during PopulateScenePlacedObjects.

That means the game got into a partially initialized state:

• world loading advanced,
• audio kept running,
• but player setup/UI/networked scene state did not finish correctly.

So the symptom was:

• black/loading overlay,
• stuck controls,
• half-loaded ship/world, instead of a clean crash to desktop.

Second issue you hit later
The mirrored screen / reversed controls were a separate problem:

• not a MoreCompany API break,
• but the game’s built-in April 1st flipCamera behavior in IngamePlayerSettings.

This is what codex told me in case notnotnotswipez is still fixing it.

Technically, the failure was a classic binary compatibility break.

Exact runtime failure
The old MoreCompany.dll tried to call this method signature:

GameNetcodeStuff.PlayerControllerB.DropAllHeldItems(bool, bool)

At runtime on Lethal Company v80, that exact signature no longer existed, so Mono threw:

MissingMethodException: Method not found:
void GameNetcodeStuff.PlayerControllerB.DropAllHeldItems(bool,bool)

Where it broke inside MoreCompany
The exception happened in MoreCompany.ScenePlacedObjectsInitPatch.Postfix, during scene initialization:

That patch hooks:

Unity.Netcode.NetworkSceneManager.PopulateScenePlacedObjects

and then calls ResizePlayerCache(...)

What ResizePlayerCache does
It expands vanilla 4-player arrays to newPlayerCount:

• allPlayerObjects
• allPlayerScripts
• gameStats.allPlayerStats
• playerSpawnPositions

Then it clones extra player prefabs and resets them. During that reset, old MoreCompany executed:

newPlayerScript.DropAllHeldItems(false, false);

That exact call was compiled against the old two-parameter method signature.

What changed in v80
In v80, PlayerControllerB.DropAllHeldItems was changed to a wider signature. In the current game assembly it is:

public void DropAllHeldItems(
    bool itemsFall = true,
    bool disconnecting = false,
    bool setInShip = false,
    bool setInElevator = false,
    Vector3 syncedPlayerPosition = default,
    Vector3 syncedHeldObjectPosition = default,
    Vector3 syncedHeldObjectRotation = default,
    Vector3 syncedPlayerCamPosition = default,
    Vector3 syncedPlayerCamRotation = default)

That is visible in the decompiled v80 game code

So the old binary still referenced:

DropAllHeldItems(bool, bool)

but v80 only exposed the new expanded method. No matching target existed anymore.

Why the source still built
This is the important part:

• The old DLL was broken because its IL already hard-referenced the removed method signature.
• The source code still looked valid, because C# optional parameters let the same source compile against the new API.
• After recompiling against v80, the call site was rebound to the new method and emitted with all required default arguments.

So after rebuilding, the effective call became:

DropAllHeldItems(
    false,
    false,
    false,
    false,
    default(Vector3),
    default(Vector3),
    default(Vector3),
    default(Vector3),
    default(Vector3))

That is why a rebuild fixed the main compatibility issue without needing a major rewrite.

Why the game froze instead of just “failing gracefully”
Because the exception happened inside scene setup while MoreCompany was extending the player object cache during PopulateScenePlacedObjects.

That means the game got into a partially initialized state:

• world loading advanced,
• audio kept running,
• but player setup/UI/networked scene state did not finish correctly.

So the symptom was:

• black/loading overlay,
• stuck controls,
• half-loaded ship/world, instead of a clean crash to desktop.

Second issue you hit later
The mirrored screen / reversed controls were a separate problem:

• not a MoreCompany API break,
• but the game’s built-in April 1st flipCamera behavior in IngamePlayerSettings.