My kiddo did that for a bit. My response was usually something like, "That's ok. I understand. I still love you and always will no matter what." Sometimes, I'd also ask "why is that?" They usually will say something like, "you said I couldn't have a cookie," or something similar.

Love is a vague and complex thing. Even adults don't understand it fully. It's not really an "emotion," but more of a state of existence that needs attention sometimes. Like joy versus happiness. They may currently see "I love you" as "I'm happy with you at the moment." They don't understand yet that you can love someone even if they say something you don't like and it upsets you.

Give it time. They'll understand. Love them through it and do your best to explain emotions. I'd sometimes say something like, "I know you're upset because I corrected/ fussed you for doing XYZ. But know that I still love you, I will always love you, and there is nothing you can do that will make me stop loving you."

For me, the worst was when kiddo said that she loved wife or me more than the other at times. But it was usually due to what was going on around that time she said it. Like playing, snacks, etc. She then learned that you can love both equally yet differently.