I was thinking more along the lines of a stadium crowd than an outdoor festival, but yes: I agree. I've had miserable luck with 2.4GHz stuff in festival environments where people camp out for a few days. :)

I don't pay very much attention to the ticket-scanning devices while I'm getting into a big show (which is generally a rather unpleasant experience on my side), but:

Don't they allow usage of 5GHz bands? Unlike 2.4GHz, I've had tremendous success with 5GHz bands in all kinds of environments -- including outdoor festivals.