I really have no idea of what caused the problem. Just wanted to let you know that someone read your post, ha.
I have to do the same thing as you (film from balcony) all the time. I think you probably isolated the problem yourself because it only occurred with your wired mic. Over that sort of length, any connection or wire problem could be the culprit - maybe even the mic.
I tried using one wireless and one wired mic exactly once and I'll never do it again! Had all sorts of problems - much worse than yours. So I use either one type or the other. Dumb as it may sound, I'd get another wireless mic.
Phil