Why did my gumbo stored in a metal pot refrigerated overnight change?

I make gumbo all the time and offered to make some for a event I was attending today. I cooked 6 gallons in three separate batches. I added them to a 8 gallon metal pot. I let it cool for a few hours and then placed it in my fridge. I also had some of the same gumbo stored in a tupperware container overnight. The gumbo in the metal pot looked completely different and had an off taste. The batch in the tupperware container tasted perfect.

I often cook large quantities of food and I have never had anything like this happen to me. I would never serve anything that was not perfect for my guests. I had to cancel the gumbo.

I would like to know if I did something wrong or if this was just a fluke. I have taken the Food Prep course and I understand the cooling issues and temps that food should be kept at.