Quesidilla chicken with off (old)taste

I had chicken quesadilla at Mugg and Bean at the airport branch two Sundays ago on 4 November and I really enjoyed it, they served it with cream cheese and avocado. So today ( 12 November at 17:30) I decided to have it at the Claremont, Cavendish branch and oh what a disappointment! When I ate it I immediately tasted that something was off in the quesadilla and I told the waiter. Claremont served it with avocado and tomato sauce - another disappointment, I didn't even taste that after I tasted the off taste in the quesidilla. He took it back and called the manager who asked me if I wanted another and I asked if they will make it with ingredients from the same container they used to make the first one and he said yes and I said no. Then he apologized. I still had the smell on my hands and when my friend smelled it she also decided not to order any food so we just had drinks. What horrified me when my friend asked the manager again about the incident is that when he tasted it he couldn't taste anything off and someone else on his staff also didn't. He was saying that it is the brown mushrooms... which I had at the airport branch and definitely not tasted off. It was definitely something that was old in the quesidilla and I am experiencing slight cramps at the moment....