I was matir neder recently (I asked a Rabbi how to do it properly) – one of the 3 lay people who were on the “beis din” told me afterwards that he misunderstood what I was being matir. I know that only one of the three people needs to know the content of the neder and the other 2 people said they understood what I was being matir. Is it fine?
You are correct. If one person knows what the neder was it is sufficient, therefore although the third person misunderstood the nature of the neder it is still valid.