While you can certainly ask, I'd like to suggest a slightly different approach for the future:
When presenting the poster, ask people who are interested in your poster (or pass by) for suggestions how to improve/critique. Often, you'll anyways get suggestions on the subject matter when discussing the poster with a visitor, and you may easily get suggestions on the presentation side of things as well in this fashion.
In my experience, the committee members devote a substantial amount of time* - but also are asked to judge/compare a large number of posters. Discussing a detailed critique with the poster author means yet increasing this amount of work, and it would be fair that not only you but all poster authors get such a critique if they ask.
Btw, sometimes poster judges are assigned a subset of posters, e.g. according to expertise, and then give scores from which the winning poster is determined - so a particular member you approach may not have evaluated your poster. However, I'd expect that they are able to do so - but then many other attendees would be able to as well. Hence the advise to talk to people who are interested in your poster or at least in the general topic.
*They have to evaluate all posters they are assigned to during the poster presentation time. In consequence, they may even skip/miss discussing posters they are interested in in detail with the author (e.g. since there are more posters to evaluate, or the interesting poster is not eligible and thus not part of the evaluation, or it is not in their share of posters to evaluate)
Being part of the poster committee is something I do as professional duty, but it is not a particularly enjoyable duty to me because it does cost me time that is particularly valuable to me: time that otherwise could go into discussing in depth a very few posters that I'm particularly interested in, or time that could go into talking in-person with colleagues (without poster) whom I meet only occasionally at such a conference.