It's because of oxidation and degradation.

If you want to avoid that awful "leftover" flavor then reheat in the oven or in a pan instead of a microwave.

I always reheat meat in the oven. Microwave makes it nasty. ?

I always notice that! Yuck!!

I doubt that Iris.

When I reheat chicken it has to be lukewarm max. If it gets hot it tastes bad!

Bebe really? Maybe I'm just a bad cook. ?

@Who Then how are you supposed to eat it? Cold or is it just bad to eat leftover meat in general?

Why have I never noticed this before? ?

I think today is the last time I eat leftover meat of any kind. It's intolerable. ?

I've always wondered this. It's especially worse with Chinese dishes containing chicken. ?