Clients wait until both teams have characters in them before they start to update CombatMissions. Character spawn messages aren't guaranteed to arrive at the same frame, so it's possible for one team to be empty at the start of the round, causing the clients to think the other team already won.

Subsurface/Source/Events/Missions/CombatMission.cs

@@ -19,6 +19,8 @@ namespace Barotrauma
 
         private static string[] teamNames = { "Team A", "Team B" };
 
+        private bool initialized = false;
+
         public override bool AllowRespawn
         {
             get { return false; }
@@ -152,8 +154,10 @@ namespace Barotrauma
 
         public override void Update(float deltaTime)
         {
-            if (crews[0].Count == 0 && crews[1].Count == 0)
+            if (!initialized)
             {
+                crews[0].Clear();
+                crews[1].Clear();
                 foreach (Character character in Character.CharacterList)
                 {
                     if (character.TeamID == 1)
@@ -165,14 +169,16 @@ namespace Barotrauma
                         crews[1].Add(character);
                     }
                 }
-            }
 
-            if (GameMain.Client == null)
-            {
-                //no characters in either team, i.e. the client hasn't received spawn messages yet
-                if (crews[0].Count == 0 && crews[1].Count == 0) return;
-            }
+                if (GameMain.Client != null)
+                {
+                    //no characters in one of the teams, the client may not have received all spawn messages yet
+                    if (crews[0].Count == 0 || crews[1].Count == 0) return;
+                }
 
+                initialized = true;
+            }
+            
             bool[] teamDead = 
             { 
                 crews[0].All(c => c.IsDead || c.IsUnconscious),