Signal stras differ from real stats

I ran a few strats on a demo account but the results where very different from the results stated on mql. How can this be?

Every broker has its own "Market Makers" and the prices differ. Not much but more than enough. Many EAs decide to open a new position if some "high" is higher than some other candle. If there is some tiny difference of 0.01, then the position is triggered on one broker but not on the other one.

Here is an example I was evaluating some time ago: