Added a bunch of checks to make sure a normalized zero vector (= NaN, NaN) is not used in any position/velocity/movement calculations. There were at least three places where it was causing problems according to error reports: when a character that can't enter a sub spawns at the center of a hull and when using an underwater scooter or throwing something while the cursor is at the position of the character, but there were tons of other places as well where it may have potentially caused physics errors.

Barotrauma/BarotraumaShared/Source/Characters/Animation/Ragdoll.cs

@@ -766,10 +766,13 @@ namespace Barotrauma
                 //this is preferable to the cost of using continuous collision detection for the character collider
                 if (newHull != null)
                 {
+                    Vector2 hullDiff = WorldPosition - newHull.WorldPosition;
+                    Vector2 moveDir = hullDiff.LengthSquared() < 0.001f ? Vector2.UnitY : Vector2.Normalize(hullDiff);
+
                     //find a position 32 units away from the hull
                     Vector2? intersection = MathUtils.GetLineRectangleIntersection(
                         newHull.WorldPosition, 
-                        newHull.WorldPosition + Vector2.Normalize(WorldPosition - newHull.WorldPosition) * Math.Max(newHull.Rect.Width, newHull.Rect.Height),
+                        newHull.WorldPosition + moveDir * Math.Max(newHull.Rect.Width, newHull.Rect.Height),
                         new Rectangle(newHull.WorldRect.X - 32, newHull.WorldRect.Y + 32, newHull.WorldRect.Width + 64, newHull.Rect.Height + 64));
 
                     if (intersection != null)
@@ -1494,7 +1497,7 @@ namespace Barotrauma
             Vector2 force = Vector2.Zero;
             foreach (Gap gap in Gap.GapList)
             {
-                if (gap.Open <= 0.0f || gap.FlowTargetHull != currentHull || gap.LerpedFlowForce == Vector2.Zero) continue;
+                if (gap.Open <= 0.0f || gap.FlowTargetHull != currentHull || gap.LerpedFlowForce.LengthSquared() < 0.01f) continue;
 
                 Vector2 gapPos = gap.SimPosition;
                 float dist = Vector2.Distance(limbPos, gapPos);