Nope. In fact, mustard loves warmth. Cold dulls its peppery kick, like putting a muzzle on a barky dog. At room temp, that zing comes roaring back.
I did a blind taste test once. Fridge mustard tasted like sad yellow paste. Counter mustard? It tasted like fireworks. Science, friends.
Also, have you ever tried to squeeze cold mustard? It’s like wrestling a frozen snake. A glob blobs out, then nothing. Room-temperature mustard flows like honey.