Just my opinion...

Many EAs will give very different results with different brokers or because of a new backtester because they are too much "pip sensitive" and then instable.

For instance it can easily happen when an EA has been optimised and that a change of a few pips in the parameters (TP or SL for instance) will make a big difference in the final result. That shows instability of the strategy.
And as different brokers have different prices (few pips but for an over optimized EA it's a big problem) it is the same problem. Same thing for a new backtester as it will modify the behaviour inside the 1M candle.

In my opinion, you should try to get similar results for different brokers or for a close range of parameters (of course results will be different but at least they should be in the same order of magnitude), and then that will show that your EA is robust to small changes.