Debug of an MT5 existing EA (i have no source code)

I don't know if what i ask is possible. I have a very good MT5 expert advisor, but it works in very different ways depending on the broker account. Actually it only works ok on a specific broker demo account, while it works in a very different (bad) way on other brokers' accounts, and even on live accounts from the same broker where it works ok on demo account. Unfortunately i don't have any source code and i even don't know in what programming language it's coded. Anyway, there must be some broker parameters that trigger different behaviours, that i can't understand as i have zero knowledge in EA programming. I also have no idea of the difficulty of the job i require, so i propose an indicative budget and am open to receiving adjusted offers.