At least I'm pretty sure that's the cause. It happens when I fail to repair something properly. I've had it happen with NPCs as well.

Exception: Collection was modified; enumeration operation may not execute. (System.InvalidOperationException)
Target site: Void ThrowInvalidOperationException_InvalidOperation_EnumFailedVersion()
Stack trace:
at Barotrauma.MapEntity.UpdateAll(Single deltaTime, Camera cam) in <DEV>\Barotrauma\BarotraumaShared\SharedSource\Map\MapEntity.cs:line 660
at Barotrauma.GameScreen.Update(Double deltaTime) in <DEV>\Barotrauma\BarotraumaShared\SharedSource\Screens\GameScreen.cs:line 247
at Barotrauma.GameMain.Update(GameTime gameTime) in <DEV>\Barotrauma\BarotraumaClient\ClientSource\GameMain.cs:line 891
at Microsoft.Xna.Framework.Game.DoUpdate(GameTime gameTime) in C:\Users\joona\Documents\Barotrauma-development\Libraries\MonoGame.Framework\Src\MonoGame.Framework\Game.cs:line 656
at Microsoft.Xna.Framework.Game.Tick() in C:\Users\joona\Documents\Barotrauma-development\Libraries\MonoGame.Framework\Src\MonoGame.Framework\Game.cs:line 500
at Microsoft.Xna.Framework.SdlGamePlatform.RunLoop() in C:\Users\joona\Documents\Barotrauma-development\Libraries\MonoGame.Framework\Src\MonoGame.Framework\SDL\SDLGamePlatform.cs:line 93
at Microsoft.Xna.Framework.Game.Run(GameRunBehavior runBehavior) in C:\Users\joona\Documents\Barotrauma-development\Libraries\MonoGame.Framework\Src\MonoGame.Framework\Game.cs:line 397
at Microsoft.Xna.Framework.Game.Run() in C:\Users\joona\Documents\Barotrauma-development\Libraries\MonoGame.Framework\Src\MonoGame.Framework\Game.cs:line 367
at Barotrauma.Program.Main(String[] args) in <DEV>\Barotrauma\BarotraumaClient\ClientSource\Program.cs:line 58