Strange behaviour with List C#

Hi I have an issue with List in my code (or something is off elsewhere). I have a class Chunk which holds some terraintiles.

I add Chunks to a List array in my main class.

 private List<Chunk> chunks = new List<Chunk>();

 Chunk newChunk = new Chunk(0, 0);
 newChunk.GRID_SIZE = GRID_SIZE;
 newChunk.TILE_SIZE = TILE_SIZE;
 newChunk.InitiateTerrain();
 
 chunks.Add(newChunk);

Then I have a help method

 Chunk getChunkAt(int xPos, int yPos) {
   foreach(Chunk chunk in chunks) {
     if(chunk.x == xPos && chunk.y == yPos) {
       return chunk;
     }
   }
   return null;
 }

This method finds Chunks, I have even logged just before the "return" statement. The if statement works, it finds chunk.x and chunk.y but if I log the chunk object, it returns null, no matter how I access it.

 chunks[0] // This returns null
 getChunkAt(0,0) // This returns null
 
 etc...

What am I doing wrong. I heard something about "as-cast" issues with C# but I dont understand what Im missing with casting. Im using List and although I cast it to (Chunk) it still turns up to null.