I have heard a story that Judas didn't actually betray Jesus willingly. It had to happen this way and Judas just played his role. Makes the story more tragic and less black and white.
The assumption here is that people will unconditionally believe and follow a person who performs miracles. But human beliefs and actions are more complex than that. People regularly refuse the evidence of their own senses, or that of knowledgeable authorities, if it contradicts their prior world view. They also regularly act contrary to better knowledge if they think it's in their interest.
So I think it's perfectly plausible that Judas experienced all of Jesus' miracles, but out of a mix of personal disappointment (Jesus not living up to Judas' expectations) and greed decided to betray him nevertheless.
There's too many alternative explanations to say that either the miracles were false xor the Judas story was false - I don't see that they're necessarily connected.